Utpal Dutt's first film, Michael Madhusudan Dutt came out. He had played the lead role. He was waiting for an opportunity to make a living as a professional actor, and this gave him that opportunity (stage acting was not financially adequate). Director Modhu Bose had seen him perform in Othello and chose him for the role. Dutt reprised the role of Michael Madhusudan Dutt in Kaliprasad Ghosh's Vidyasagar, which came out in the same year, and then in Modhu Bose's Mahakabi Girish Chandra.

He joined IPTA (Indian People's Theatre Association) in early 1951. He joined the Central Calcutta Squad, managed by Ritwik Ghatak. During his 10-month stint at IPTA, he acted in plays like Tagore's Bisarjan, Officer, Panu Pal's Voter Bhet, Dalil, and Bhanga Bandar. He had to sever ties with IPTA due to political differences, but the stint demonstrated to him the importance of theatre for the common man. He was to devote a large part of his life to writing and directing political theatre which spoke to the common people and urged them to rebel against oppression. His group LTG switched to staging Bengali plays instead of English. Around this time, Utpal and LTG briefly dabbled in Jatra and street theatre. Over time, theatre became a tool for Utpal to further his political ideology. He would proudly brand himself a "propagandist", using theatre as a vehicle for revolutionary change rather than merely entertainment.

At the behest of his soon-to-be wife Shobha Sen, Utpal Dutt started writing plays. Wrote his first play Chhayanot, which was staged at Biswarupa in December 1958. He took lease of the Minerva Theatre for 99 years, effectively making it the base of operations for LTG. In 1959, his play Angaar , based on a coalmine disaster, gained massive popularity, running over a hundred shows and traveling to other parts of India. It was Dutt's first big success as a playwright-director. Married fellow actor and dramatist Shobha Sen in 1961. That year, Dutt famously voiced for Uttam Kumar as Othello in a scene from the film Saptapadi. Jennifer Kapoor voiced Suchitra Sen as Desdemona.
He debuted as a filmmaker with Megh (1961), a psychological thriller in which he played the lead. His play Ferari Fouj was received with universal acclaim, leading him to be honoured by the Sangeet Natak Akademi Award in 1963. His historic play Kallol based on the naval mutiny of 1946, premiered in 1965. It critiqued the role of Indian National Congress in the naval mutiny, causing a stir in political and cultural circles. His second film Ghoom Bhangar Gaan (1965) premiered and was met with critical acclaim. He featured in Merchant-Ivory's Shakespeare Wallah, his first non-Bengali film, co-starring his guru Geoffrey Kendal and his family. While the Kendals played versions of themselves, Utpal played an Indian Maharajah.
He later wrote an article in Desh Hitaishi magazine criticising the establishment, leading to his arrest in September 1965 on charges of sedition under the Defence of India Act.

Dutt was freed in early 1966 after seven months of imprisonment. Arrested again briefly the following year while shooting for Merchant Ivory's film Guru at the Taj Hotel, Bombay. A warrant had been issued against him following his play Teer, which was about the Naxalite movement. In his book Towards a Revolutionary Theatre, Utpal Dutt claimed that he was in Bombay to receive "delivery of weapons for the revolution" in addition to filming Guru. He was subsequently arrested at the Taj and flown back to Calcutta. Eventually released at the intervention of Merchant Ivory's unit to complete filming Guru. Turned down the Sangeet Natak Akademi award for best director in 1966.

His first Hindi films Bhuvan Shome and Saat Hindustani both came out in 1969. His first collaboration with Mrinal Sen, Bhuvan Shome portrayed him as a portly bureaucrat finding a distraction from his humdrum existence when he goes on a hunting trip and forges an unusual friendship with a tribal woman. By the time Bhuvan returns, he is (seemingly) transformed. Utpal's performance was widely acclaimed and won him his first and only National Film Award for Best Actor. K.A. Abbas saw a production of Kallol in Calcutta, which led him to cast Utpal Dutt as the Punjabi ex-army man in Saat Hindustani. Dutt had to employ an accent to make the role believable, which was quite the feat considering his elite Bengali and western upbringing. His proficiency in Urdu/ Punjabi stemmed from the time he spent as a child with Pathan Regiment of the army while his father was posted in Berhampore.
In 1970, LTG (Little Theatre Group), which Dutt founded and helped build, folded up due to in-fighting and political differences. He founded a new troupe called People's Little Theatre (PLT).

Dutt appears in his first mainstream Hindi film, Guddi (1971), directed by Hrishikesh Mukherjee. It was his first team-up with Mukherjee, with whom he'd go on to form a successful collaboration. The film featured Dutt as the congenial uncle of the hero, who is faced with a curious problem: that his girlfriend is in love with the film actor Dharmendra. Dutt's character attempts to demonstrate to her that films exist in a make-believe world. Around the same time, he appeared in Mrinal Sen's Calcutta 71 (1972), Tarun Majumdar's Sriman Prithwiraj (1973) and Ritwik Ghatak's Jukti Takko aar Gappo (1974).
His famous play Tiner Talowar, an allegory about late 19th century Bengali theatre came out in 1971 and became an immediate sensation. This was followed by Barricade (1972), Dutt's play depicting the conflict between the Nazis and communists in Germany as a stand-in for the Congress-Communist feud in India. A staging of Duswapner Nagari (1974), a play about pre-Emergency political violence, was attacked by political goons and the players were beaten up.

Dutt's major Hindi outings in 1975 included Julie, Do Anjaane and Amanush, the latter being his early appearance as an antagonist. First collaboration with Satyajit Ray in The Middleman/ Jana Aranya, a film, as Dutt noted later, was a veiled protest against the excesses of the Emergency. This early run-in with the maestro left its impact, and Dutt admired Ray's unobtrusive directing style. Their collaborations continued with Joy Baba Felunath/ The Elephant God (1980) and Hirak Rajar Deshe/ Kingdom of Diamonds (1980). The latter strongly resonated with Dutt as it was an allegory about an absolute state and a despotic rule trying to brainwash the masses, in which Ray self-admittedly commented against the Emergency years. Utpal played the despot with aplomb. According to Utpal Dutt, The Kingdom of Diamonds was Ray's only out-and-out political film.
1979 saw the release of the one film that makes Utpal Dutt a recognisable face among Bollywood fans. Ironically and somewhat reductively, Dutt's most well-remembered stint in Hindi films is as the industrialist Bhavani Shankar in Hrishikesh Mukherjee's Gol Maal. His remarkable comic timing and precision was a demonstrable output of his theatre days, and his chemistry with Amol Palekar who played the lead role, is a testament to the fact that both were a product of the stage. This was followed by Naram Garam, a spiritual sequel to Gol Maal, and Shakti Samanta's Barsaat Ki Ek Raat.

The 1980s were marked by a series of portrayals as corrupt zamindars, moneylenders, politicians and capitalists in Hindi and Bengali potboilers, punctuated by relatively wholesome roles as middle-class patriarchs in Hrishikesh Mukherjee (Rang Birangi, Lakhon ki Baat, Kissi Se Na Kehna) or Basu Chatterjee (Shaukeen, Apne Paraye, Hamari Bahu Alka, Kirayadaar) films. Besides these, he continued to feature in arthouse classics like Goutam Ghose's Paar and Padma Nadir Majhi., alongside Satyajit Ray's Agantuk/ The Stranger. In The Stranger, he played Ray's alter ego, an ageing globetrotter who returns home after a long sojourn abroad and in his outpourings mirrors Ray's own (and often Dutt's) view of the world. Padma Nadir Majhi, a poignant chronicle of the lives of fishermen whose livelihood revolved around the Padma river, turned out to be Utpal Dutt's cinematic swansong. In 1991, the playwright in him uncannily foreshadowed the Babri Masjid incident and the unrest that followed one year later in his play Janater Aphim (Opium of the Masses), in which religious extremists bring down a mosque which has been allegedly built on top of a temple.
Utpal Dutt passed away on August 19, 1993.