Manoj was born as 'Manoj Tuli' on 11 July 1960. He studied at the Bishop Cotton School in Simla. His father, Rajendra Kumar, was a popular actor in the 1960s and 1970s. Rajendra Kumar died of cancer in 1999.
While shooting for his debut movie, Love Story with Vijayta Pandit, the duo got romantically involved. The relationship later came to an end as tensions arose between the Pandit and Kumar families.
In 1984, Manoj married Namrata Dutt, daughter of Sunil Dutt and Nargis and sister of actor Sanjay Dutt. The couple has two daughters, Saachi and Siya. Saachi is married to Bilal Amrohi, the grandson of filmmaker Kamal Amrohi.
Manoj and his brother-in-law Sanjay Dutt worked together in two films, Naam and Kaante.
He made his film debut with Love Story (1981). This film played at the box office for a long period of time; not only for its innovative story, but also its music and the debutants. Many youngsters began to emulate his character in the film, produced by his father and directed by Rahul Rawail which was a blockbuster. His next film, the 1982 release Teri Kasam with actress Poonam Dhillon, another heart-throb of the generation, was a moderate success. That same year he starred in the musical Star which failed at the box office but its music was popular.
He then worked in Mahesh Bhatt's Janam in (1985). His understated performance in this film is still considered his career's best. In the following year he had his second box office hit with Naam (1986), again a Mahesh Bhatt film which was produced by his father and also starred his brother-in-law Sanjay Dutt in the lead role. Despite the success of Naam, Manoj's career declined as all of his subsequent films failed to do well at the box office.
He has been successfully paired with almost all young ladies of ’80s – Poonam Dillon, Rati Agnihotri, Neelam, Vijeyta Pandit, Madhuri Dixit and Padmini Kolhapure. Yet his pairing with Vijeyta Pandit in their debut movie is still remembered most. His revival project, Phool with the top actress Madhuri Dixit, couldn’t give success though its melodious songs were noticed.
Having produced his earlier films Janam and Naam, his father tried to revive his career with the 1993 film Phool which also had his father and father-in-law Sunil Dutt in supporting roles. However, it didn't bring him any luck either. He took a long break from acting in the mid 1990s. In 2000, he returned to films with the delayed release Gang which had been in production for nearly a decade.
In 2002, he played one of the six protagonists in the crime thriller Kaante, directed by Sanjay Gupta and a remake of the Hollywood hit Reservoir Dogs (1992). Kaante was a huge success at the box office and the third highest-grossing film of 2002.
In 2004 he appeared in his first American film, Guiana 1838. This award winning film by Rohit Jagessar grossed the highest screen average at the North American box office on opening weekend and is among the Top 25 all-time highest screen average charts. Guiana 1838 tells the story of Indians arriving in the British colony of British Guiana, now Guyana, as indentured servants amidst the abolition of slavery during the nineteenth century.
In 2009, he starred in the silent film My Daddy Strongest.1986: Nominated: Filmfare Award for Best Actor – Janam