She made her first theatrical debut in Düsseldorf Schauspielhaus, to her father's utter disapporval. However, her mother and grandmother were supportive of her decision to become an actor and accompanied her as she toured to act in Weimar, Chemnitz, and Aachen.

From 1908 to 1913, Thea von Harbou was a member of the cast at Hoftheater Weimar, a theatre with which maestros such as Goethe, Schiller and Lizst were associated with in the previous century.

Her novel Die Nach uns Kommen (translation: Those Who Come After Us) was published in 1910 and received considerable success. For the next three years, she was associated with the renowned German theatre Vereinigte Stadttheater Chemnitz.

She used to work with Stadttheater Aachen for a brief period, where she was under the direction of her future husband, Rudolf Klein-Rogge.

On this day, she married Rudolf Klein-Rogge, who was a theatre actor at that time. The couple lived together in Nuremberg for two years, where she gave up acting and became a full-time writer. The couple lived together in Nuremberg for two years, where she gave up acting and became a full-time writer.
She, along with her husband Rudolf, had moved to Berlin by 1917. While on the move as an actress, she expanded her literary repertoire by publishing various short stories, animal tales, fairy tales, and full-length novels. Her engagement with epic themes and mythology deepened over time. With the advent of war, her writing adopted a pronounced nationalistic orientation, characterized by patriotic narratives aimed at bolstering morale. Her novels emphasized themes of sacrifice and duty, particularly among women, while extolling the glorious dignity of the fatherland.

She first met Joe May (standing in the middle of the photograph) during this period and thus began her career in films.
Late in 1918 or early in 1919, von Harbou met Joe May—and through May, a brief time later, Fritz Lang. Two years older than the director, she was already well-established as an author in her own right. According to her own account of things, von Harbou happened to read a brief newspaper item announcing that one of her stories had been bought by May-Film GmbH. She phoned her publisher right away, asking for an explanation. He put her in contact with Joe May, who was preparing to direct Die heilige Simplizia (St. Simplicia), the first of several features the producer-director would adapt from von Harbou's work. Up to this time von Harbou had not given much thought to motion pictures, but now she plunged into writing scenarios for Joe May. One job swiftly led to another. Her fiction output slowed down. In short order she would become one of Germany's most celebrated film writers, not only because of her partnership with Fritz Lang, but also for writing scripts for F. W. Murnau, Carl Dreyer, E. A. Dupont, and other German luminaries.

She met Fritz Lang, who was yet to make a name for himself in the film world, and they began collaborating on several projects. She and her then-husband Klein-Rogge divorced and the former began an affair with Fritz Lang, who was married at that time.

Thea von Harbou met Fritz Lang during the preparation for the adaptation of her novel Das indische Grabmal (The Indian Tomb, 1918), for which Lang was initially slated to direct. However, Joe May ended up directing the film in two parts titled The Indian Tomb, Part I: The Mission of the Yoghi and The Indian Tomb, Part II: The Tiger of Eschnapur. Following this, von Harbou became the screenwriter for all of Lang's films from Das wandernde Bild (The Wandering Image, 1920) through to Das Testament des Dr. Mabuse (The Testament of Dr. Mabuse, 1933).

The book by von Harbou was adapted again— in 1938 by Richard Eichberg and eventually in 1951 by Fritz Lang himself.

The Wandering Image, the first collaboration between Lang and von Harbou is released.
The film exists in fragmentary state today but boasts of having an ingenious non-linear screenplay— a rarity for cinematic storytelling of that time.

Four Around The Woman, a lesser-known film in the ouvre of Lang-Harbou is released. The film has a convoluted plot that confused the critics and audience alike. It depicts the ruthless underbelly of the city and the idea of double-crossing, functioning as a precursor to the themes the duo would explore more elaborately in Dr. Mabuse films.
The film was considered "lost" and was restored in 1987, after it was discovered in Cinemateca Brasileira in São Paulo, with Portuguese intertitles.

"After Das wandernde Bild, Lang and von Harbou rushed into a picture for Decla called Kdmpfende Herzen (Fighting Hearts), but also known as Die Vier um die Frau (Four Around a Woman). Shown in February of 1921, this film has often been overlooked within the Lang-von Harbou canon, partly due to its long-standing status as a lost work, only recently rediscovered. Now that it is available for viewing, Four Around a Woman emerges as a first-rate piece, showcasing the evolution and refinement of Lang's journey as a filmmaker. Von Harbou's intricate storytelling techniques harmonized seamlessly with Lang's grand directorial vision. Both were fond of employing framing devices, layered flashbacks, digressive asides, abrupt transitions, and stylistic cutaways.

The adaptation of Harbou's adventure novel The Indian Tomb was released in two parts, under direction of Joe May. They were titled The Indian Tomb and The Tiger of Eschnapur.

The Indian Tomb is the film that Fritz Lang had wished to direct in the early 1920s, but to his chagrin, the project was taken over by producer Joe May and Lang was hired as a co-writer. May, captivated by Thea von Harbou's novel, not only agreed to produce the film but also took on the directorial role after Lang had suggested him for the production. May's version of The Indian Tomb, like the later adaptations by Richard Eichberg in 1938 and Lang himself in 1959, was split into two parts and featured high production values that successfully captured the enchanting atmosphere and the ambitious narrative von Harbou had created. The story explores the collision between European 'rationality' and the mystique of India, a theme that resonated deeply at the time owing to the somewhat problematic fascination with Orientalism. The film emerged during a post-war period when obsession with all things Indian was at its peak, with even film companies drawing inspiration from Indian philosophy—such as Prana, the production company behind F.W. Murnau's Nosferatu (1922), named after the Hindu concept of the universal life force.

Thea von Harbou and Fritz lang finally get the chance to write an original story of a film together, without any interference of a studio or any other external element. The film, titled Destiny (Der müde Tod in German language) is a meditation on the concept of "death" and they began writing the story in the wake of Lang's mother's death. United by a common fascination for Indian philosophy and mythology, the duo finds the inspiration for the plot in the folk story of Savitri.

Destiny had deep influence on some of the greatest filmmakers that came after Lang.

Luis Buñuel once said that the film, "Opened my eyes to the poetic expressiveness of the cinema. When I saw Destiny, I suddenly knew that I wanted to make movies." He later referenced Destiny in a scene in his experimental masterpiece Un Chien Andalou (1929).

For his film The Seventh Seal (1957), Swedish filmmaker Ingmar Bergman drew inspiration from the personification of Death as played by Bernhard Goetzke in Destiny.

For Hitchcock, this Lang-Harbou collaboration became the yardstick for the storytelling possibilities offered by cinematic medium.

The idea of defying death multiple times as shown in Destiny has also seeped into post-modern films, such as Tom Tykwer's 1998 film titled Run Lola Run.

Harbou and Lang's next release was Dr. Mabuse, The Gambler, which was released in two parts a month apart. With this film, the duo had created a prototype—a convoluted plot set in a dog-eat-dog world of ruthless gangsters, femme fatales and dark alley— that would culminate into the noir genre that would pervade Hollywood cinema in the 1940s.

While the film was adapted from an on-going serialised novel by Norbert Jacques, von Harbou and Lang took creative freedom to deviate from several elements of the novel in order to write a film about debasement of German society after the First World War and how it breeds a warped supervillian like Dr. Mabuse, who presciently carried several similarities to Hitler. For instance, Mabuse's involvement with peddling counterfeit currency was enunciated in the film, which served as a reference to the diminishing value of Deutsch Mark as a result of hyperinflation due to Germany having to pay war reparations in the wake of the First World War..

Thea von Harbou and Fritz Lang got married after having an affair for almost two years. Her ex-husband, Klein-Rogge, continued to act in several of Lang's films.

The next project von Harbou embarked upon was writing the screenplay for Fritz Lang's Die Nibelungen, which was divided into two parts and released as Die Nibelungen: Siegfried and Die Nibelungen: Kriemhild's Revenge.The film served as a celebration of a national epic as against the morally and financially decaying Germany post-First World War. The film is based on Der Ring Des Nibelungen, which is Wagner's operatic interpretation of the Teutonic epic poem written around 1200 A.D.

This film struck a chord with Hitler and Goebbels. When the Nazis came to power, Lang's film— which exemplified a modern hero fighting the course of nature organically to rise as an Übermensch without the backing of gods— became an apt allegory and a justification for the cause of Hitler. In 1929 the National Socialist paper Der Angriff praised Die Nibelungen as a "film of German loyalty." In his speech of March 28, 1933, at the Kaiserhof, Goebbels praised the film. During that same year, the Nazis authorised a re-release of Siegfrieds Tod, featuring a voice-over by Theodor Loos, one of Lang's recurrent actors, who had played King Gunther.

In what was billed as "Fritz Lang Gives His Last Interview" in New York City's Village Voice (August 16, 1976), published during the month of his death, the director was still trying to explain away the implications.* Questioned by Gene D. Phillips about Die Nibelungen, Lang patiently explained, "When I made my films, I always followed my imagination. By making the Siegfried legend into a film, I wanted to show that Germany was searching for an ideal in her past, even during the horrible time after the First World War in which the picture was made. To counteract the pessimistic spirit of the time, I wanted to film the great legend of Siegfried so that Germany could draw inspiration from her epic past, and not, as Mr. [Siegfried] Kracauer suggests, as a looking-forward to the rise of a political figure like Hitler or something stupid of that sort. I was dealing with Germany's legendary heritage—just as in Metropolis, I was looking at Germany in the future.""

Thea von Harbou also wrote screenplays for films by several other renowned directors such as F.W. Murnau, Johannes Guter, Carl Theodor Dreyer and Arthur von Gerlach . These screenplays were mainly adapted from novels.
For Johannes Guter, she wrote a screenplay of the adventure-drama film Princess Suwarin (1922), adapted from a Ludwig Wolff novel.

For Murnau, she wrote the screenplays of The Burning Soil (1922), Phantom (1922), The Expulsion (1923) and The Finances of the Grand Duke (1924).

For Dreyer, she wrote the screeplay of Michael (1924). It was one of the initial films to covertly delve into the theme of homosexuality.

For Arthur von Gerlach's historical-drama film Chronicles of the Gray House (1925), she wrote a screenplay based on Theodor Storm's novella titled A Chapter in the History of Grieshuus.

When von Harbou began working on the novel version of Metropolis in 1925, it was aimed to be issued in a complete book form as a tie-in to the film's release in various promotional materials. However, it was published earlier in Das Illustrierte Blatt in the form of serialised novel, beginning August 1926.

Metropolis was released under the banner of Parufamet, which was a collaborative company formed by Paramount, MGM and UFA, as the portmanteau suggests. This collaboration took place as Germany's UFA was undergoing immense loss and USA's Paramount and MGM joined hands to loan money to UFA under certain conditions.

Filming for Fritz Lang's ambitious Expressionist futuristic dystopian masterpiece Metropolis lasted for around eighteen months, with a high budget that cost than five million Reichsmarks. Both Lang and von Harbou co-wrote the screenplay based on latter's novel, which was written under the presumption that the book will be converted into a film. For the final screenplay, a lot of material originally present in von Harbou's novel, involving occultism and magic was ommitted.

In 1927, she wrote the novel titled Spione (English title: Spies) and in conjunction its screenplay version for the Fritz Lang film of the same name, which was released on 22 March, 1928. For the first time since 1920, von Harbou received the sole credit of screenwriting.

The spy stories had already been a part of the popular culture, owing to the popularity of literary characters such as Sherlock Holmes, Ashenden and C. Auguste Dupin. But what Thea von Harbou's Spies does is take the spy story into the modern world of technology, with the characters always being heard or seen through the watchful eyes of technological possibilities. The novel and the subsequent film influenced the genre greatly by prefiguring the proto-Bond franchise in a certain sense.

Late in November, von Harbou and Lang travelled to Vienna to attend the premiere at Ufa-Tonkino, which also marked their last collaboration in silent cinema— Die Frau im Mond (Woman in the Moon). This film, too, was based on a science-fiction novel penned von Harbou who later converted it into a screenplay alongside Lang.

"At a press conference, the two were asked about the advent of talking pictures, and their future prospects. Neither Lang nor Thea von Harbou were willing to commit to doing a film totally equipped with sound. According to an article in Mein Film, von Harbou expressed their mutual reservations. "She is just as unenthusiastic about one hundred percent talking pictures as Fritz Lang is; he believes that a special style must be developed before talking pictures can be made... that are artistic and effective."
Lang, however, offered tantalizing remarks. He said his next motion picture would be vastly "influenced by sound." Even more intriguing, Lang assured Mein Film that the subject matter, which was already settled and promised to be "especially interesting," would satisfy those clamoring for him to direct a film with "roots in Vienna." This is a fascinating hint that M, Lang's masterpiece—which started out as a story about a writer of poison-pen letters— might have taken its first form with a Viennese backdrop."

M, a thriller directed by Fritz Lang is released. Thea von Harbou, again, receives the sole credit for the screenwriting. It must have been a daring task to bring a tale about child murders and implied molestation on screen in the early 1930s, but Lang's magnum opus, complemented by von Harbou's brilliant script, does not shy away from discussing these primal fears. The film, which further went on to become a blueprint for many serial killer films, is also known for its nuanced portrayal of the perpetrator not demonised as a force of evil who commits crime in cold blood but as someone who shows remorse for the crime he was forced to commit due to his deranged mind.

By the end of 1931, the NSDAP (Nazi Party) had already established its foothold in Berlin and found many people siding with it, including Thea von Harbou and even her ex-husband, Rudolf Klein-Rogge.

Noted Lang biographer Patrick McGilligan wrote, "Lang's wife had always been a conservative nationalist, while at the same time she demonstrated progressive tendencies; she was an early, outspoken advocate of legalized abortion in Germany, an activist for reform in sex discrimination legislation, a proponent of equal rights for women. Throughout the 1920s she worked tirelessly on behalf of these causes, behaving in some ways as the very opposite of an extreme right-winger.
Now Thea von Harbou, according to people who knew her, grew infected by the Nazi vision. The fatherland's defeat in World War I was a trump note in NSDAP propaganda. America's cultural invasion of Germany, especially in the motion picture field, was also a bothersome issue raised by the nationalists. Von Harbou admired the Nazi pageantry and symbolism. Gradually, so gradually that, for a while, it escaped Lang's notice, his wife was swept away."

Thea von Harbou and Fritz Lang ended their marriage after 13 years. Whether it was von Harbou's association with NSDAP or her affair with the young Indian-born journalist Ayi Tendulkar is the reason for calling the marriage of is a matter of speculation.

"Lily Latte had become Fritz Lang's mistress, and that Thea von Harbou and Tendulkar were likewise developing an intimacy. Worse, his nonviolent, left-wing friend Tendulkar (who, like von Molo, once had lived for a spell in Gandhi's ashram), began to spout the same National Socialist nonsense as Thea von Harbou. The NSDAP had made an unlikely alliance with the Indian community in Berlin and elsewhere in Germany. The two groups were united in their hatred of the British, and the Berliner Gandhians were willing to overlook anti-Semitism and other hard-line Nazi atrocities in return for unconditional support for their Nationalist revolution at home."

The Testament of Dr. Mabuse, co-written by Lang and von Harbou was released after several censorships by Goebbels' newly set up board. It was also Lang's last films made in Germany as he escaped the country in the wake of rising fascism. Both Hitler and Goebbels had been admirers of Lang's earlier films and the Goebbels even proposed, according to Lang's somewhat dubious accounts, that he should make propaganda films for the party.

After her divorce with Fritz Lang, Thea von Harbou continued to be a significant asset of Nazi Party, directing some propaganda films and receiving scenarist credits for several other films. Her name was mentioned in the diaries of Goebbels, who had an affinity and respect towards her and described her as "a very clever woman".
It remains uncertain whether von Harbou was the hard-headed Nazi that Lang frequently described her in interviews. Unlike many other film personalities of the Hitler era, she never publicly expressed ideological commitments in newspapers or magazines. Her relatives maintain—just as von Harbou herself claimed in statements to Allied captors after World War II—that her motivations were thoroughly patriotic and that she joined the Nazi Party mainly to support Indian immigrants in Germany, including her husband.
Nevertheless, she remained a highly productive screenwriter, and her career continued uninterrupted for the next decade. In a system where every film was effectively backed by the state, Thea von Harbou received screenwriting credits on approximately twenty-six films and provided uncredited contributions to numerous others—including several propaganda films for Nazi Germany.

She was briefly detained by in a British interrogation camp where she was interrogated about her relations with NSDAP.

In postwar Germany, all prominent figures who had joined the NSDAP (Nationalsozialistische Deutsche Arbeiterpartei or National Socialist German Workers' Party) fell under suspicion. As a result, Thea von Harbou was detained from July 10 to October 10, 1945, in Staumühle, a British-run prison camp. Her relatives argue that the length of her detention was partly due to her authorship of a novel advocating for Indian independence, which may have displeased British authorities.
Von Harbou was undeniably a staunch nationalist, and Allied interrogation records document her acknowledged memberships and activities during the Nazi era. In her defense, she asserted that she had only joined the Nazi Party in 1941 to support Indians in Germany and Indian prisoners of war, emphasizing that she never worked explicitly for the Party and refrained from attending Party meetings, ignoring multiple warnings. According to her account, her direct contributions to the government were limited to volunteer efforts, including welding, manufacturing hearing aids, and providing emergency medical care. Notably, she was awarded a medal of merit for rescuing individuals during two air raids.

She was possibly banished from the film industry for a brief period of time due to her allegiance to Nazi Party. By the late 1940s, Thea von Harbou was writing screenplays for the German-dubbed versions of films produced by Deutsche London Film. Some of the remarkable films she worked on include Carol Reed's The Third Man, Alexander Korda's An Ideal Husband, and Ludwig Berger's The Thief of Bagdad. In addition, Harbou authored serialized novels, such as Der Fernfahrer und der Teufel, which was published in the newspaper called Berliner Morgenpost in 1952. She also wrote three screenplays that exemplified the diversity of German post-war cinema: one for the anti-war film Es kommt ein Tag (English translation: A Day Will Come) in 1950, another for Dr. Holl (English title: Affairs of Dr. Holl) in 1950 or 1951, and a third for the regional film Dein Herz ist meine Heimat (English translation: Your Heart Is My Homeland) in 1953.

At the age of sixty-five, she was invited to the Berlinale as a guest of honor in 1954, where she appeared at the screening of her film Der müde Tod (English translation: Destiny). There, she eagerly answered the questions asked by the audience after the screening. A relative stated later that she was overjoyed by the experience of watching the film that she did not pay attention to the steps as she was departing from the venue. She tripped and fell and eventually developed a serious hip injury as a result. She was then taken to a hospital where she died some days later on 1st July, 1954.

According to Elfriede Nagel, her last secretary, her funeral was attended by government officials, Ufa representatives, and several film and theater personalities, along with devoted fans. Director Ludwig Berger, who had once fled Hitler but later returned to Europe, honored her memory by calling her a "Queen in giving." Von Harbou was laid to rest in Charlottenburg, and eventually, the city of Berlin took over the maintenance of her grave.