Stringer married Elyse Buxbaum, a museum administrator, in a civil ceremony at City Hall in New Haven. He said in a statement that it was an "incredibly meaningful day" for the couple.
Connecticut allows same-sex unions and New York does not.
New Haven Mayor John DeStefano Jr. officiated the Sept. 2 marriage ceremony between Buxbaum and Stringer. The couple had a religious ceremony in Manhattan on Sept. 5.
New York's state Senate killed a bill that would have allowed same-sex marriage.