She acted in the Bengali film Aranyer Din Ratri directed by Satyajit Ray; Padatik by Mrinal Sen. She is also known for her celebrity talk show, Rendezvous with Simi Garewal.

[6] Simi grew up in England and studied at Newland House School with her sister Amrita.

Her fluency in the English language induced the makers of the English-language film Tarzan Goes to India to offer her a role.

During the 1960s and '70s, she was in several notable Indian films, working with leading directors such as with Mehboob Khan in Son of India (1962), Raj Khosla in Do Badan (1966), Raj Kapoor in Mera Naam Joker (1970), Satyajit Ray in Aranyer Din Ratri (1970, Days and Nights in the Forest) and Mrinal Sen in Padatik (1973, The Guerilla Fighter).

She starred opposite Shashi Kapoor in Columbia Pictures' Siddhartha (1972), an English-language movie based on the novel by Hermann Hesse.

Garewal did a nude scene in this film which caused some controversy in India and was only released for exhibition after complying with cuts ordered by the Indian Censor board.

[15] After the Mumbai terrorist attacks of November 2008, Simi Garewal aroused controversy by publicly calling for the Indian government to "carpet-bomb" the training camps in Pakistan for which she later apologized.