Mernissi was born into a middle-class family in Fez in 1940. She received her primary education in a school established by the nationalist movement, and secondary level education in an all-girls school funded by the French protectorate. In 1957, she studied political science at the Sorbonne and at Brandeis University, where she earned her doctorate. She returned to work at the Mohammed V University and taught at the Faculté des Lettres between 1974 and 1981 on subjects such as methodology, family sociology and psychosociology. She has become noted internationally mainly as an Islamic feminist.

As an Islamic feminist, Mernissi is largely concerned with Islam and women's roles in it, analyzing the historical development of Islamic thought and its modern manifestation. Through a detailed investigation of the nature of the succession to Muhammad, she casts doubt on the validity of some of the hadith (sayings and traditions attributed to him), and therefore the subordination of women that she sees in Islam, but not necessarily in the Qur'an.

As a sociologist Mernissi has done fieldwork mainly in Morocco. On several occasions in the late 1970s and early 1980s she conducted interviews in order to map prevailing attitudes to women and work. She has done sociological research for UNESCO and ILO as well as for the Moroccan authorities. In the late 1970s and in the 1980s Mernissi contributed articles to periodicals and other publications on women in Morocco and women and Islam from a contemporary as well as from a historical perspective.

In 2003, Mernissi was awarded the Prince of Asturias Award along with Susan Sontag.

Mernissi is currently a lecturer at the Mohammed V University of Rabat and a research scholar at the University Institute for Scientific Research, in the same city.

Mernissi’s first monograph, Beyond the Veil, was published in 1975. A revised edition was published in Britain in 1985 and in the US in 1987. Beyond the Veil has become a classic, especially in the fields of anthropology and sociology on women in the Arab World, the Mediterranean area or Muslim societies in general. Her most famous book, as an Islamic feminist, The Veil and the Male Elite: A Feminist Interpretation of Islam, is a quasi-historical study of role of the wives of Muhammad. It was first published in French in 1987, and translated into English in 1991. For Doing Daily Battle: Interviews with Moroccan Women (1991), she interviewed peasant women, women labourers, clairvoyants and maidservants. In 1995, Mernissi published a memoir, Tales of a Harem Girlhood.

Other works of Mernissi include :

• Islam and Democracy: Fear of the Modern World (1992)
• Forgotten Queens of Islam
• Scheherazade goes West
• Islam, Gender and Social Change
• Women's rebellion & Islamic memory (Atlantic Highlands, N.J. : Zed Books, 1996.)