The daughter of socialist parents, Jenny and "Mac", Mary was born in Hampstead, north London, and educated at High Wycombe School and St Anne's College, Oxford University; graduate student in sociology, University of California at Berkeley.
Her essay on The homosexual role in 1968 may have started lesbian and gay studies in Britain. "Her argument that society labels people as deviants in order to exert control over them pre-dated Michel Foucault's similar work, which is now so much better known."
Mary and her then partner Elizabeth Wilson were active in building and shaping the UK Gay Liberation Front, which erupted at the London School of Economics in the autumn of 1970. Both were engaged in the earliest protests, campaigns, marches and working groups. Later their attentions turned towards creating bridges between the women's movement and the lesbian movement.
Mary's work on issues of gender and sexuality played a significant role in influencing a generation of sociologists. I wrote to her as an undergraduate when she was teaching at Leicester University and she sent me several of her unpublished papers on the sociology of homosexuality, in which she applied the ideas of the US sociologist Talcott Parsons to the study of homosexuality.
Within feminism, Mary developed a critique about family life, and with Michèle Barrett wrote The Anti-Social Family (1982).
After her retirement in 1996, she more or less left academia behind, working for some time at the Citizens Advice Bureau in Islington, north London, and continuing her political activities. Her papers have been catalogued at the London School of Economics.
Mary Susan McIntosh died aged 76 of a stroke. She is survived by her partner of 23 years, Angela Stewart-Park; and by her son, Duncan Barrett, with her former partner, Michèle Barrett.