He married Damyanti Sahni, also known as Dammo, who would go on to become an important collaborator and an integral part of his public life. She acted alongside Balraj in Dharti ke Lal (1946) and another film called Gudia (1947).

Balraj Sahni taught Hindi and English at Rabindranath Tagore's Santiniketan. He joined the institution despite the meagre salary, as he deeply admired Tagore. During this period, he staged several plays and earned Tagore's appreciation. Until then, he had been writing short stories in both Hindi and English and had already earned a strong reputation. It was Tagore who encouraged him to begin writing in Punjabi. Sahni went on to write several books in Punjabi, and his work regularly appeared in the popular Punjabi magazine Preetlari.

Sahni worked with Mahatma Gandhi for a year. He was invited to Sevagram to join the editorial staff of Nayi Talim, a magazine published under the Wardha Scheme of Education, which was backed by Gandhi. Sahni held Gandhi in the highest regard and considered it a privilege to work with and be around him. This experience had a profound influence on his worldview. It was at the behest of Lionel Fielden, the then director of All India Radio, and with Gandhi's approval, that Sahni set off for London to join the Indian section of the BBC.

Both Balraj and Damyanti joined BBC London as Hindi announcers. During his time there, Sahni was introduced to Marxist thought and Russian cinema, both of which deeply influenced him. He became disillusioned with the lack of realism in American films and turned to Russian cinema for inspiration. Driven by communist ideals, these films depicted class struggles and the daily battles of ordinary men and women. They became a major source of creative and ideological inspiration for Sahni, shaping his belief that Marxism and Leninism offered solutions to many of humanity's problems. It was also during this period that he was introduced to the concept of “People's Theatre,” a form of drama created by and for the working class, focusing on their concerns and struggles.

He returned to India with the idea of working in films. He bumped into Chetan Anand, who offered him a role in his latest film, Neecha Nagar. Though the role didn't materialise, Sahni found himself increasingly drawn to the world of cinema. He was also inducted into the Indian People's Theatre Association (IPTA), of which he soon became a prominent figure. He was asked to direct Khwaja Ahmad Abbas's first play, Zubeida, and acted in Mohan Segal's Jadu Ki Kursi.

He acted in Khwaja Ahmad Abbas's directorial debut, Dharti Ke Lal, which was IPTA's only film venture. The film's realistic depiction of farmers during the famine was pathbreaking for its time. It was also the first Indian film to be dubbed and released in Soviet Russia. That same year, filmmaker Phani Majumdar cast both Balraj and his wife Damyanti in the film Door Chalen.

Balraj and Damyanti acted together in Gudia, a film adaptation of Henrik Ibsen's A Doll's House, directed by Achyutrao Ranade.

Damyanti Sahni passed away at the age of 26. She had contracted a form of amoebic dysentery during the shoot of Dharti Ke Lal, possibly from drinking contaminated water.

His first major film was Hulchul, directed by S.K. Ojha and produced by K. Asif, in which he co-starred with Dilip Kumar and Nargis.

Chetan Anand invited him to write the screenplay and dialogues for the next Navketan production, Baazi, which was to be directed by a new filmmaker named Guru Dutt, a friend of Dev Anand.

Guru Dutt and Balraj Sahni had differing approaches to cinema, which led to several disagreements during the writing of Baazi. For Sahni, the structural integrity of a screenplay was paramount, while Guru Dutt placed greater emphasis on song sequences. Although Sahni had already included six song situations in his script, Guru Dutt added a few more, which drove a wedge into their working relationship.

During a bus commute, Sahni came across a talented conductor named Badruddin Qazi. It was Sahni who advised him to barge into Guru Dutt's office pretending to be a drunkard and create a scene—an impromptu audition that won him the role in Baazi. Badruddin was later given the screen name Johnny Walker. While Baazi did not fully align with Sahni's politics and worldview at the time, he nonetheless infused the script with elements of social justice, realism, and the destitution he had explored during his time with IPTA.

Around the same time, Zia Sarhadi's Hum Log was released alongside Guru Dutt's Baazi. Sarhadi had seen Sahni perform in an IPTA play called Sadak Ke Kinare and had originally written the story of Hum Log for K. Asif. However, when he narrated it to Chandulal Shah of Ranjit Studio, Shah was so impressed that he took the project from Asif and handed it to Sarhadi to direct. Although Dilip Kumar was the original choice for the lead role, it ultimately went to Balraj Sahni. Initially unsure of himself, Sahni later experienced a moment of clarity that gave him the conviction to carry the part with confidence.

Balraj Sahni was at the beach with his children when Asit Sen, Bimal Roy's assistant, approached him with a message: Roy wanted to meet him. Sahni dressed up for the occasion in his finest London suit, powdered his face, and went to see Bimal Roy. However, Roy was disappointed—Sahni's appearance didn't match the image he had in mind for the protagonist of his next film. Hrishikesh Mukherjee narrated the story to him. After hearing the narration of Do Bigha Zamin, Sahni went to Jogeshwari, a slum inhabited by north Indian buffalo herders and tenders. He observed their gait, speech, posture, and how they wore their turbans. This keen observation helped him prepare for the role of a rickshaw puller in Do Bigha Zamin. He insisted on doing his own makeup and choosing his costume. When he finally presented himself to Roy, he had completely transformed into Shambhu Mahato, the peasant. Roy was deeply impressed, and this transformation added a great degree of authenticity to Sahni's performance.

In one scene, Sahni's character had to fall at the feet of the zamindar, played by Murad, and beg him to spare his land. Unbeknownst to Sahni, Bimal Roy had instructed Murad to suddenly jerk his feet away. Murad ended up kicking Sahni hard in the face. Shocked and humiliated, Sahni began sobbing in anger. Murad immediately rushed to embrace him and explained the situation.

Amiya Chakravarty's Seema was acclaimed for its performances and won Nutan her first Filmfare award. Sahni was paired with her for the first time. In the same year, he was also cast in Garm Coat, the first film of Cine Co-operative, a consortium consisting of Balraj Sahni, Rajinder Singh Bedi and Geeta Bali, among others. It was an adaptation of Nikolai Gogol's short story titledThe Overcoat.

Lal Batti was another film produced by Cine Co-operative, and the only film Balraj Sahni ever directed. He was drawn to the theme of the film becaue of his deep interest in social realism and a passion to tell stories of common people. He co-directed the film with Krishan Chopra. The film didn't work and the consortium had to be shut down. Sahni never directed another film after this.

Bhabhi (1957), directed by the Tamil filmmaker duo Krishnan-Panju, is a family drama about the widowed Ratanlal (Balraj Sahni) who weds Shanta (Pandari Bai) to tend to his younger brothers and sisters. When the young brothers grow up, their bickering brides cause rift in the family. For Balraj, who would eventually find great success playing patriarchs, this was one of his early outings as the family elder. The film was a success, counted as one of the highest grossers of the years.

Sone Ki Chidiya, produced by Ismat Chughtai, was based on a story written by her. The film was directed by Shahid Latif, who was also Chughtai's husband. It featured a poem recited by Kaifi Azmi, with Balraj Sahni lip-syncing to the words. The poem, “Aaj ki raat bahut garm hawa chalti hai,” would later foreshadow Sahni's swansong, the film Garm Hawa (1973).

Balraj Sahni also starred in Kader Kapoor's Devar Bhaabi this year, alongside Mala Sinha and Rajendra Kumar.

Lekhraj Bakhri's Chand saw Balraj Sahni in a period drama set against the backdrop of royal customs and polygamy. He played a dignified but conflicted royal physician in this social drama that questioned oppressive traditions.

Anuradha was Balraj Sahni's second film with Hrishikesh Mukherjee, following Musafir, Mukherjee's directorial debut. It also marked the debut of Leela Naidu, a former Miss India pageant winner. The film was based on a short story by Sachin Bhowmick, who co-wrote the screenplay with Rajinder Singh Bedi. Anuradha also marked Pandit Ravi Shankar's return to Hindi cinema as a composer, following his earlier work in Dharti Ke Lal and Neecha Nagar. Balraj Sahni's performance as the dutiful doctor received widespread acclaim.

Bimal Roy's Kabuliwala was his tribute to Rabindranath Tagore. Sahni felt a deep connection to Tagore and his larger-than-life persona. His time at Santiniketan allowed him to engage more closely with Tagore's ideas, deepening his admiration and respect for the poet. The film, based on Tagore's short story, explores the bond between an Afghan dry-fruit seller and a little girl. To prepare for the role, Sahni disappeared from home a couple of weeks before shooting and took up accommodation in a colony of Pathans in Sion. He learned their language, studied their demeanour and body language, and poured it all into his portrayal of Abdul Rahman Khan.

Bhabhi Ki Chudiyan, directed by Sadashiv J. Row Kavi, had Balraj Sahni playing the ideal elder brother, whose love for his younger sibling shapes the film's emotional core. Quiet and dignified, His performance lent depth to this gentle family drama about relationships, sacrifices, and the quiet strength of tradition and affection within a household.

Anpadh was an attempt to spread the message of educating the girl child. In the film, Sahni appeared in a rare negative role. He played the heroine's brother, who loved her deeply but did not see the value in giving her an education — in fact, he became an obstacle to it. Jawaharlal Nehru, the then Prime Minister, was a strong proponent of women's education, and the film was designed to promote that message. The music by Madan Mohan is considered one of his most notable works.

Many artists affiliated with communism felt betrayed when China waged war against India. Though they had sympathised with China's brand of communism, the conflict left them disillusioned. As a result, several left-leaning actors chose to participate in Chetan Anand's Haqeeqat. Balraj Sahni, an avowed leftist, was among them, along with Kaifi Azmi, M.S. Sathyu, and Shaukat Kaifi.

Waqt, one of Hindi cinema's first popular multi-starrers, featured Balraj Sahni as the patriarch of a family that disintegrates and finds each other by the end of the film.

Sahni joined hands with his old IPTA compatriot Salil Chowdhury for Pinjre ke Panchhi, which was the latter's directorial debut. It remains the only film Salil Chowdhury ever directed.

Aasra (1966), adapted from a short story by Protiva Bose, was earlier made in Bengali as Madhya Raater Tara (1966). The story follows orphaned Shobha (Mala Sinha) as she navigates life in a relative's household, facing indifference and subtle exploitation. Balraj Sahni shines as Dr. Surendranath Kumar, a compassionate, progressive patriarch whose empathy and moral clarity anchor the film. His principled support for Shobha, even against familial and societal pressures, provides the emotional backbone and ethical compass of the story.

Sunghursh was an adaptation of Mahasweta Devi's Layli Admaner Aayna, a Bengali novella about a family of thugs in 19th-century Benares. Sahni's role had shades of grey and placed him opposite a young Sanjeev Kumar, while also reuniting him with Dilip Kumar after Hulchul (1951).

Raj Khosla's Do Raaste cast Balraj Sahni as the family patriarch, with Rajesh Khanna and Prem Chopra playing his brothers. This was one of two films released in 1969, along with Aradhana, that elevated Rajesh Khanna to superstardom. By this time, Balraj was frequently playing father figures who were pivotal to the story and screenplay.

Balraj's son Parikshit was brought forth as leading man with Pavitra Paapi, in which Balraj also played a central character. Parikshit, who had apprenticed under Russian director Sergei Bondarchuk on the TV epic War and Peace in the 1960s, had written the screenplay of Pavitra Paapi with the intention of directing it, but it was later handed over to Rajendra Bhatia.

In Paraya Dhan, Balraj Sahni once again plays a grey character who has shady past that his family is not aware of. He plays a hitman who leaves the world of crime to raise his daughter.

Hindustan Ki Kasam was a war drama directed by Chetan Anand, in which Sahni appeared as part of an ensemble cast. The film was ostensibly designed to replicate the success of Haqeeqat, but it ultimately fell flat.

Garm Hava, a Partition tale, featured Sahni as the patriarch of a Muslim family grappling with the question of whether to migrate to Pakistan. The film's title was taken from the same Kaifi Azmi poem used in Sone Ki Chidiya (1958). Based on a story by Ismat Chughtai, the screenplay was adapted by Kaifi Azmi and Shama Zaidi, who was also the wife of the film's director, M.S. Sathyu. All three — Kaifi, Shama, and Sathyu — were associated with the Indian People's Theatre Association (IPTA).

The story, centred on an Indian Muslim's inner conflict during the Partition, created a stir upon completion. It was held up by the Censor Board for nearly 11 months due to the political sensitivity of its subject. Balasaheb Thackeray, founder of the Shiv Sena, requested a special screening before its release to assess its message. After watching the film, he approved its release, satisfied that it upheld the idea of an Indian Muslim being part of the national mainstream.

The following year, Garm Hava won the Nargis Dutt Award for National Integration. It is widely considered one of Balraj Sahni's most powerful and enduring performances.

Balraj Sahni passed away from a heart attack on 13 April 1973 in Bombay, just a day after finishing his work on Garam Hawa. His death was also preceded by the emotional trauma of losing his daughter the previous year. His lifelong commitment to social realism and emotive performances in landmark films redefined Indian cinema's portrayal of the common man, and his legacy continues to inspire generations of artists and storytellers.