“That’s not how we experience our lives,” she said.

Ms. Bonauto would be the first to say she builds on the work of others. As early as the 1970s, gay couples began suing for the right to marry, inspired by the 1967 Supreme Court ruling in Loving v. Virginia, which struck down state laws banning interracial marriage. In 1983, a young Harvard law student named Evan Wolfson wrote his third-year thesis on why gays should be free to marry.

Mr. Wolfson was eventually hired by Lambda Legal, the gay advocacy group, where he joined what he called “a very small little network of people who at that time were dedicated to toppling the so-called sodomy laws” that criminalized homosexual sex. Among them was Ms. Bonauto.

The daughter of a pharmacist and a preschool teacher from Newburgh, N.Y., she had come out, with some difficulty, while an undergraduate at Hamilton College. There, Ms. Bonauto was harassed over her sexual orientation, which she said contributed to her desire to “make life better” for others.

By 1990, with a law degree from Northeastern University, she was working for GLAD in Boston. She had been there less than a week when a gay couple approached her with the idea of suing to get married. She said no, the timing was not right.

“I would have cases of somebody who goes to a Dunkin’ Donuts and the wait person realizes it was a gay person and goes nuts,” Ms. Bonauto recalled. How could she pursue a seeming luxury like marriage, she reasoned, when gay people were being discriminated against in housing, employment and adoption and being harassed by the police?

In 1991, a Honolulu lawyer, Dan Foley, did what Ms. Bonauto had declined to do and sued on behalf of three same-sex couples denied marriage licenses. The case prompted intense discussion in gay legal circles, recalled Mr. Wolfson, who later became Mr. Foley’s co-counsel and has since founded Freedom to Marry, a national advocacy group. Some, he said, thought marriage was “patriarchal and exclusionary,” while others said the gay rights movement “was supposed to be about liberation,” not joining heterosexuals. Still others, like Ms. Bonauto, worried that the legal foundation had not been laid and that a loss could lead to a gay rights setback.

She was right to worry; Hawaii voters eventually amended their Constitution to allow a ban on same-sex marriage, much as California would. So the advocates opened up what Mr. Wolfson called “a second front” in Vermont — in part, he said, because the legal and constitutional climate was more hospitable there, and in part “because we had a really terrific talent in Mary.”