The 46-year-old actress, who plays Miranda Hobbes in "SATC" walked down the aisle in a Carolina Herrera custom-made dress, reported People magazine.
The couple, who met at an education rally in 2002, tied the knot three years after getting engaged at the Love, Peace and Marriage Equality rally in New York City.
"On May 27, 2012, Cynthia Nixon and her girlfriend, Christine Marinoni, were legally married in the state of New York. Nixon wore a custom dress by Carolina Herrera," the actress' representative confirmed.
Nixon and her education activist fiancee waited to say their "I do's" until same-sex marriage was legal in New York state. It hadn't been legalized when the couple were engaged, but became legal last summer.
Nixon and 45-year-old Marinoni have a son together named Max Ellington Nixon-Marinoni, whom the latter gave birth to in February 2011.
The actress has two children, daughter Samantha and son Charles Ezekiel, from a previous relationship with Danny Mozes.