Buoyant gay couples cheered by supporters began marrying Sunday on the landmark day that New York became the sixth and largest state to recognize same-sex weddings and provided fresh energy to the national gay rights movement.

After days of contentious negotiations and last-minute reversals by two Republican senators, New York became the sixth and largest state in the country to legalize gay marriage, breathing life into the national gay rights movement that had stalled over a nearly identical bill here two years ago.