Brother of the retired Indian diplomat Aftab Seth, Roshan Seth studied at St. Stephen's College in Delhi, where he developed a liking for theatre, especially Shakespearean plays, following which he attended the London Academy of Music and Dramatic Art. After studying British repertory theatre, Roshan's first play was Peter Brook's 1972 production of Shakespeare's play A Midsummer Night's Dream. Subsequently, he made his feature film debut in the 1974 British crime suspense Juggernaut, playing the role of Azad. His next movie came after 8 years, in 1982, with the British-Indian epic biographical movie Gandhi, where he was seen playing the role of Pandit Jawaharlal Nehru, which won him the BAFTA Award nomination for Best Actor in a Supporting Role.

After Gandhi, Roshan was flooded with movie offers and was seen in movies like Indiana Jones and the Temple of Doom, A Passage to India, My Beautiful Laundrette, and Partition. He was also part of Doordarshan's 53-episode series titled Bharat Ek Khoj in 1988, where he played the role of Jawaharlal Nehru and was also the anchor. The actor continued to be a part of Indian as well as international projects such as Stalin, Street Fighter, Bombay Boys, Monsoon Wedding, Kabul Express, Guru, and Ek Tha Tiger.