Millett's Sexual Politics (1970) began as a doctoral thesis and became the book that put second-wave feminist theory on the bestseller list.
Its central move is definitional. Politics, she argued, should be understood as power-structured relationships in general, not merely as the business of parties and parliaments — and on that definition the relation between the sexes is political, because it is a relation of dominance and subordination maintained by institutions, socialization and, where those fail, force. Patriarchy on her account is the most pervasive ideology of any culture and its most fundamental concept of power, and it survives revolutions in property and government untouched because it operates in the family, which liberal politics treats as private.
The second half of the book is a critical demolition that made it famous: close readings of D. H. Lawrence, Henry Miller and Norman Mailer showing how sexual dominance is not merely depicted in their work but celebrated, and how literary reputation had been assembled around it. Mailer's furious reply, The Prisoner of Sex, did more for the book than any review.
She was also an artist and a memoirist. Flying (1974) and Sita (1977) wrote about her own life, including her bisexuality, with a candor that cost her; The Loony-Bin Trip (1990) is an account of her forced psychiatric treatment and her decision to stop taking lithium, and stands as an early first-person critique of psychiatric coercion. She spent much of her later life running an art colony for women in upstate New York, largely outside the academy her book had transformed.