Kate Kendell, executive director of the National Center for Lesbian Rights, said Martin died at a San Francisco hospital Wednesday morning, two weeks after a broken arm exacerbated her existing health problems.
Her wife, Phyllis Lyon, was by her side, Kendell said.
"I am so lucky to have known her, loved her and been her partner in all things. I am devastated, but I take some solace in knowing we were able to enjoy the ultimate rite of love and commitment before she passed," Lyon said.
Along with six other women, they founded a San Francisco social club for lesbians in 1955 called the Daughters of Bilitis. Under their leadership, the group evolved into the nation's first lesbian advocacy organization.
The couple were married at San Francisco City Hall on June 16. Mayor Gavin Newsom, who officiated the wedding, singled them out to be the first gay couple to legally exchange vows in the city, in recognition of their activism.
The two were among the two dozen couples who served as plaintiffs in the lawsuits that led the state Supreme Court to overturn California's ban on gay marriage in May.
The Daughters of Bilitis was named after book of lesbian erotic poetry first published in Paris in 1894.
Martin and Lyon also became active in the National Organization for Women in 1967, and Martin became the first openly gay woman elected to the group's board in 1971, reports CBS affiliate KPIX-TV in San Francisco.
San Francisco Superior Court Judge Donna Hitchens, a founder of the National Center for Lesbian Rights, said, "Del lived her life with great compassion, wit, tenacity, generosity and valor. She inspired thousands of us to be more courageous and energetic than we thought possible."
Martin was born in San Francisco in 1921 as Dorothy L. Taliaferro and attended George Washington High School, the University of California at Berkeley and San Francisco State College. She married James Martin at age 19 and had a daughter, Kendra, two years later.
The marriage ended in divorce after four years and she met Lyon in Seattle in 1950 when both were working for the same magazine. The two began sharing a household together in San Francisco on Valentine's Day in 1953.
In 1995, U.S. Sen. Dianne Feinstein, D-Calif., and Congresswoman Nancy Pelosi, D-San Francisco, named Martin and Lyon as delegates for the White House Conference on Aging.