Jean O'Leary (March 4, 1948 – June 4, 2005) was an American gay and lesbian rights activist. She had been a Roman Catholic Religious Sister before this involvement, and would later write about her experience in a 1984 anthology, Lesbian Nuns: Breaking Silence.
O'Leary was born in Kingston, New York, and raised in Cleveland, Ohio. In 1966, just out of high school, she entered the novitiate of the Sisters of the Holy Humility of Mary, in order to "have an impact on the world." In 1971, after graduating from Cleveland State University with a degree in psychology, she left the convent, before completing the period of training.
O'Leary then moved to New York City and did doctoral studies in organization development at Yeshiva University. During that period, she became involved with the nascent gay rights movement, joining the Gay Activists' Alliance (GAA) Chapter in Brooklyn and later lobbying state politicians. In 1972, feeling that it was too dominated by the men of the movement, she left the GAA and founded Lesbian Feminist Liberation, one of the first lesbian activist groups in the women's movement. Two years later, she joined the National Gay Task Force, negotiating gender parity in its executive with director Bruce Voeller and joining as co-executive director.
In 1977 O'Leary organized the first meeting of gay rights activists in the White House through arrangements made with White House staffer Midge Costanza. She was the first openly gay person appointed to a presidential commission, the National Commission on the Observance of International Women's Year, by Jimmy Carter. In this role she negotiated for gay and lesbian rights to be included on the discussion in a conference marking the year in Houston, Texas.
O'Leary was among the first openly gay delegates to a national political convention, attending the United States Democratic Party convention in 1976. She also served on the Democratic National Committee for 12 years, 8 of those on the Executive Committee, another first.
During the early 1980s O'Leary focused on building National Gay Rights Advocates, then one of the largest national gay and lesbian rights groups. It was one of the first to respond to the HIV/AIDS epidemic's implications for legal and civil liberties, using aggressive litigation to ensure AIDS patients' access to treatment.
O'Leary died in San Clemente, California of lung cancer, aged 57. She was survived by her partner, Lisa Phelps, their daughter Victoria, their son David de Maria, his life partner James Springer, and David's and James' son, Aiden de Maria.
Radical lesbian feminism and transgender exclusion
O'Leary was criticized for advocating for the exclusion of transgender women from the gay and lesbian rights movement. At the 1973 Christopher Street Pride rally, O'Leary criticized Sylvia Rivera and referred to her as a man.  Following O'Leary's statements, Rivera attempted suicide. 
- "Jean O'Leary, 57, Former Nun Who Became a Lesbian Activist", New York Times, June 7, 2005, retrieved November 8, 2012
- Marcus, Eric (1992). Making history : the struggle for gay and lesbian equal rights : 1945-1990. HarperCollins. ISBN 0-06-016708-4.