Simi Garewal was born in Delhi in an Army family; her father became a Brigadier in the Indian Army. She was brought up in London. She came back to India as a teenager and made her film debut with the English film Tarzan Goes to India (1962) opposite Feroz Khan. She was then offered many other roles. She appeared in Mehboob Khan's Son of India (1962), Raj Kapoor’s Mera Naam Joker (1970), Satyajit Ray’s Aranyer Din Ratri (1970), Mrinal Sen’s Padatik (1973) and Raj Khosla’s Do Badan (1966).

She was also a part of Columbia Pictures' Siddhartha, an English film inspired by Hermann Hesse’s novel of the same name.  She also gave a special appearance in Kabhi Kabhie (1976) and this was followed by Chalte Chalte (1976) in the same year. Garewal is best remembered for her negative role in the Subhash Ghai film Karz (1980) where she starred opposite Rishi Kapoor and Prem Nath.

In the 1980’s, Garewal turned to production and direction. She created It’s A Woman’s World,  a TV show for Doordarshan. She also made a documentary for Channel Four UK on Raj Kapoor titled Living Legend Raj Kapoor.  This was followed by another documentary on Rajiv Gandhi called India’s Rajiv. She also wrote and directed the Hindi film Rukhsat (1988). Garewal created and hosted the talk show Rendezvous with Simi Garewal. She returned to TV with the talk show India’s Most Desirable in 2011.