The ceremony, held at sunset at a private home, was attended by a small group of family and friends of the couple, including Parker's mother and Hubbard's sister, according to a statement from Parker's office.
"This is a very happy day for us," said Parker, the first openly gay mayor of a major U.S. city. "We have had to wait a very long time to formalize our commitment to each other. Kathy has been by my side for more than two decades, helping to raise a family, nurture my political career and all of the other ups and down and life events that come with a committed relationship."
Late Thursday she tweeted: "I am privileged to now be the wife of the woman I have loved for more than 2 decades. I couldn't be happier. We said our vows today.-A"
The Rev. Paul Fromberg administered the vows. He is a friend of the couple and partner of Parker's longtime political consultant Grant Martin, formerly of Houston. Fromberg and Martin now live in San Francisco.
Thursday was the couple's 23rd anniversary.
"It's wonderful," said City Councilwoman Ellen Cohen. "They've demonstrated a commitment to each other over all these years. How marvelous it is that they can look forward to a long life together as a married couple. I'm very happy for them."
Parker had previously said that she would not get married until the union was legal in Texas, including as recently as June, when the U.S. Supreme Court struck down the federal Defense of Marriage Act. Speaking in November, however, it was clear the mayor had reflected on the impact of the verdict.
"At some point I fully intend to marry her," Parker said. "I will say that when the Supreme Court ruling came down, the first person to call me was my youngest daughter, who said, 'Does this mean you're going to go out and marry mommy now?' And I said, 'Well it doesn't exactly mean that because it doesn't change everything.' But, you know, I also am conscious of the messages I send to my own kids."
When Parker first took office in 2009, she pledged to put the city before social advocacy. Conservatives have accused her of reneging on that pledge, particularly in 2012 when she joined 78 mayors in 2012 in calling for equal marriage rights for gay couples.
And in late November, Parker, relying on a legal opinion from City Attorney David Feldman and recent court rulings, announced the city would begin offering health and life insurance benefits to the spouses of all legally married city employees, gay or straight, in alleged violation of a 2001 city charter amendment.
At the time, Parker said the decision would not affect her because she and Hubbard were not legally wed, adding that Hubbard pays about $700 a month for health insurance. In Thursday's statement about her marriage, however, Parker clarified that Hubbard has other insurance options available and will not claim city benefits.
"Why does she wait to get married in another state after the election? Why does she give same-sex benefits to couples married in other states after the election?" Woodfill said. "This is a mayor who is bringing California and New York values to Texas, and these are values Texans don't subscribe to. Texans have defined their position on marriage in the form of a constitutional amendment."
Nationally, Parker often is seen as the gay mayor of Houston. She has worked to ensure she is seen as the mayor who happens to be gay, repeatedly saying, "The best thing I can do for my community is to be a great mayor of Houston."
Parker and Hubbard met in 1990 when Hubbard, a tax consultant, stopped by Parker's Montrose bookstore, Inklings, looking for clients. They have two daughters and a son, and their goddaughter lives with them.