Aged four, Kensit appeared in a television advert for Birds Eye frozen peas. In 1972, she had her first role in the film For the Love of Ada. Her next film role was two years later in The Great Gatsby starring with Mia Farrow, whom she would later portray in the 1995 biopic Love and Betrayal: The Mia Farrow Story.

A pupil at the Italia Conti Academy stage school, Kensit's first starring roles were in British children's television programmes such as The Adventures of Pollyanna (1982) and Luna. She also appeared as Estella in a BBC adaptation of Great Expectations in 1981.

She started to come to fame in 1985, leading a dual career as the lead singer of the band Eighth Wonder and an actress. Eighth Wonder had two Top 40 singles ("I'm Not Scared" UK #7 and "Cross My Heart" UK #13) and appearing on Top of the Pops, while Kensit also starred as Eppie in an adaptation of Silas Marner, with Ben Kingsley. At the time, Kensit at the height of her fame infamously stated: "All I want is to be more famous than anything or anyone".

In 1986, she won the lead female role in the film version of Absolute Beginners, based on the book by Colin MacInnes. In 1988, Eighth Wonder had their only UK top 10 hit with "I'm Not Scared", which was written and produced by the Pet Shop Boys.

Although the band's success quickly waned, the song appeared in the 1989 film Lethal Weapon 2, in which Kensit, now focused solely on being an actress, played Rika van den Haas, a South African consulate secretary with whom cop Martin Riggs (played by Mel Gibson) falls in love.

Following Lethal Weapon, she gave what many observers considered her best performance in 1991's little seen Twenty-One. Of her role, Variety magazine wrote, "Fans of Kensit get plenty of her; her lovely face and form are always the center of attention. The cool control with which she executes the role is admirable".

In 1992, she had a leading role in the British film "Blame it on the Bellboy" as Miss Carolyn Wright, a desperate real estate dealer in Venice who would stop at nothing to clinch a deal. In 1995 Kensit starred in Angels & Insects, with Kristin Scott Thomas and Mark Rylance, which was nominated for an Academy Award for Costume Design and in which she complied with director Philip Haas' request to bleach her pubic hair.

Kensit's last major lead film role was in the Newcastle based The One and Only, which failed to get wide distribution.