Sullivan Alioto taught school for six years before being elected to the School Committee, first as a teacher of disabled children in Harlem and Bedford-Stuyvesant, then at the John Marshall School in Boston's Dorchester neighborhood, where she taught children with behavioral issues. While serving on the School Committee, Sullivan Alioto earned her doctorate at Harvard. She is credited with having been a dedicated member of the School Committee Sullivan Alioto worked full-time to improve the quality of the school. Sullivan Alioto was regarded as the "most liberal" of the five members of the Boston School Committee when, in December 1974, it voted 3-2 to refuse to comply with the order of Federal District JudgeWendell Arthur Garrity Jr. to desegregate the Boston Public Schools. At the height of the School Committee debates over whether to comply with the Federal Court order to desegregate the Boston Public Schools, in 1974 and 1975, Kerrigan was the leading liberal on the committee, as described in Newsday by reporter John Treen, "the argument is between Kerrigan and Sullivan. Sullivan is the most liberal of the Committee, Kerrigan the most vocally conservative. Kerrigan accuses Sullivan of questioning an appointment... Sullivan explodes." The University of Massachusetts, Boston, in a report as part of its Collaborative History of Segragation in Boston, described Sullivan Alioto as "an outsider" who "entered the Boston School Committee in 1974 and completely challenged the status quo, altering the committee for the better.... By taking a look at Kathleen Sullivan’s role in the move to desegregate Boston Public Schools, we gain an often overlooked narrative because of how she did not quite fit in with her contemporaries at the time." Sullivan Alioto was succeeded on the school committee by her sister, Jean Sullivan McKeigue.
From 1974 to 1976, Sullivan Alioto dated the then-closeted Barney Frank. In April 1976, Sullivan Alioto's father suggested that, while she was attending a convention in San Francisco, she lunch with former San Francisco MayorJoseph Alioto. She and Alioto married in 1978 and remained together until his death in 1998. Because Alioto was divorced, the wedding was performed by excommunicated Catholic priest and activist Joseph O'Rourke. Sullivan Alioto has two children, Patrick Joseph Sullivan Alioto and Domenica Alioto.