Posing on a rooftop in the Big Apple, Nixon, 46, wore a flowing, pale green gown by Carolina Herrera and carried a bouquet of white peonies. Marinoni, 45, wore a suit with a darker green tie for the ceremony.
The couple got engaged in 2009, but waited to marry until it was legal in New York state, which happened last summer.
The Sex and the City actress and the education activist have a 1 ½-year-old son named Max together.
Nixon also has two children from her previous relationship with photographer Danny Mozes.