She attended Hofstra University (then Hofstra College) where she also received a master's degree in English in 1964. She married Robert M. French Jr. in 1950; the couple divorced in 1967. She later attended Harvard University, earning a Ph.D in 1972. Years later she became an instructor at Hofstra University.

In her work, French asserted that women's oppression is an intrinsic part of the male-dominated global culture. Beyond Power: On Women, Men and Morals (1985) is a historical examination of the effects of patriarchy on the world.

French's 1977 novel, The Women's Room, follows the lives of Mira and her friends in 1950s and 1960s America, including Val, a militant radical feminist. The novel portrays the details of the lives of women at this time and also the feminist movement of this era in the United States. At one point in the book the character Val says "all men are rapists". This quote has often been incorrectly attributed to Marilyn French herself. French's first book was a thesis on James Joyce.

French was diagnosed with esophageal cancer in 1992. This experience was the basis for her book A Season in Hell: A Memoir (1998).

She was also mentioned in the 1982 ABBA song, "The Day Before You Came". The lyrics that mentioned French were: "I must have read a while, the latest one by Marilyn French or something in that style".

French died from heart failure at age 79 on May 2, 2009 in Manhattan, New York City. She is survived by her son Robert and daughter Jamie.