Kitty Lambert, 54, and Cheryle Rudd, 53, from Buffalo, New York, were married just after midnight Saturday at Niagara Falls' State Park's Luna Island, near the U.S.-Canada border.
The women, with five grown children between them from previous marriages, were joined by several hundred friends, family, supporters and even a group of tourists for the first marriage of two members of the same sex since New York became the sixth, and largest, U.S. state to legalize gay marriage.
Lambert, an art gallery manager, wore a blue satin dress she sewed herself, while Rudd, who works in a food processing plant, opted for a white tuxedo with tails. The grandmothers have been a couple for over a decade.
The civil ceremony, which followed a service conducted before midnight by Jewish, Baptist and Episcopal clergy members, was officiated by Niagara Falls Mayor Paul Dyster.
By the time Dyster reached "by the laws of the state of New York," his words were drowned out by thunderous applause.
Lambert choked up during the religious service, answering unequivocally "yes, yes, yes!" when asked if she was making the choice of her own free will.
The women danced on stage after being married to Lady Gaga's "The Edge of Glory."
In honor of the first ceremony, the world-renowned water cascade was lit with rainbow-colored lights in a colossal, shimmering hommage to the multicolored gay pride flag.
Tourists who happened upon the ceremony and the attendant crush of media were delighted.
"This is pretty cool," said Australian Andrew Holder, adding "You come to see the falls, you see history."
"Serendipity is amazing," echoed Adam Jowicz of Birmingham, England.
Earlier, the women said their marriage represented a major step for gay rights in the United States, with Lambert calling it "an amazing moment."
"We're achieving that real American Dream to be treated like everybody else and be protected under all those laws."
Former state senator Sam Hoyt, who recently resigned to work for Gov. Andrew Cuomo, called his vote on the issue "the most important, significant vote I ever took."