NEW YORK (FOX5NY) - The 255th annual New York City St. Patrick's Day Parade kicked off Thursday morning along 5th Avenue in Manhattan.
Some 200,000 marchers participated.
Former Sen. George Mitchell, who brokered the Northern Ireland Peace Accord, served as the Grand Marshal.
The weather was expected to hold up for the duration of the parade.
The forecast called for sunny skies to start with temperatures in the upper 50s. By mid-afternoon, skies would become cloudier with highs in the low 60s. The parade ends at 4:30 pm just as thunderstorms were expected to roll in.
NY & US Merchant Marine Acad Reg Band LI, NY pic.twitter.com/yKONvknu16— St Pat's Parade NYC (@StPatsParadeNYC) March 17, 2016
For 20 years, Irish-American Emmaia Gelman had been on the sidelines of the storied parade every March, protesting instead of participating.
But on Thursday, Gelman finally marched up Fifth Ave. A year after a limited easing of the parade's prohibition on gay groups, organizers opened the lineup more broadly to include activists who protested the ban for years.
"This is a massive victory," says Gelman, 41, who was repeatedly arrested at parade protests and met her longtime partner at one.
The change stands to close a long chapter of controversy at the largest and oldest U.S. celebration of Irish heritage, which was broadcast live in Ireland and the United Kingdom for the first time. Besides marking firsts, this year's parade also looked back, honoring the centennial of Ireland's Easter Rising against British rule.
Organizers aimed to invoke "the lessons of sacrifice and heroism, of love and tolerance, embodied in the Irish spirit," parade board chairman John Lahey said when the plans were announced.
Tracing its history to 1762, the parade features about 200,000 marchers.
For years, organizers said gay people could participate but couldn't carry signs or buttons celebrating their sexual identities. Organizers said they didn't want to divert focus from honoring Irish heritage.
Irish gay advocates sued in the early 1990s, but judges said the parade organizers had a First Amendment right to choose participants in their event.
Over the years, activists protested along the route, and some politicians boycotted. The pressure grew in 2014, when Mayor Bill de Blasio refused to march, and Guinness and Heineken withdrew their sponsorships.
The sponsorships resumed when parade organizers opened a door to gay groups last year, allowing a contingent from parade sponsor NBCUniversal. But critics saw the gesture as tokenism.
Meanwhile, Boston's St. Patrick's Day parade ended a ban on gay groups that organizers had successfully defended at the Supreme Court. In the ensuing months, gay marriage became legal throughout the U.S. and Ireland.
Against that backdrop, New York St. Patrick's Day Parade organizers said they'd add a second gay group this year to the parade ranks: the Lavender & Green Alliance, which had long protested the gay-group ban.
Some longtime parade participants have balked at the arrival of gay delegations.
"It's contemptible," said Bill Donohue of the Catholic League, who stopped marching last year.
But de Blasio, a Democrat, joined the parade Thursday because of its new inclusiveness. So did Gelman, an American studies doctoral student, great-granddaughter of Irish immigrants and a member of Irish Queers, a group that marched with the Lavender & Green Alliance.
She participated with her partner, whose birthday is St. Patrick's Day.
With the Associated Press