With a landmark Supreme Court decision on same-sex marriage expected in the coming weeks, the District’s 40th annual jam-packed, rainbow-studded Capital Pride Parade featured a float with a gay couple tying the knot.

Marriott International, which sponsors the parade, arranged for longtime couple George Carrancho and Sean Franklin — who met in Texas, where same-sex marriage is illegal — to marry atop one of the floats. The couple currently resides in New York, where gay marriage is legal, but they wanted to make a statement in Washington.

By 4 p.m., scores of people wearing rainbow colors crowded Metro’s Red Line to Dupont Circle, where the massive, boisterous crowd jostled to exit the platforms.

Outside, the neighborhood was awash with spectators — organizers said tens of thousands of people lined the 1 1/2 -mile route that passes many of the city’s well-known gay restaurants and clubs — cheering as bands marched, hip-hop and reggae beats pounded and motorcycles rolled displaying pride flags. Some in the crowd waved posters that read: “Born This Way” and “I love my kids, gay and straight.”

Robert Shooltz, 32, who is straight, came from McLean and endured an hour-long trip on Metro, with a 20-minute delay, to get to the march. “This is so important for human rights and equality in general,” he said immediately after purchasing a pride bandana.

Scott Miles, his 3-year old son, Coltrane, his wife Melissa and their 1-year old daughter, Molly, watch a dancer perform at Dupont Circle before the Capital Pride Parade. (Brittany Greeson/The Washington Post)

It was a special day for first-time parade-goer Maria Ortiz, of Silver Spring. She came out to her family earlier this year.

Growing up Catholic, she said, she feared judgment from her family and friends, and at one point was suicidal. She came not only to support gay rights and same-sex marriage but to feel others’ support.

“I have never been around so many people like me,” she said. “I am already feeling the love.”

The day’s festivities began with a rooftop “vow renewal” ceremony that called on everyone present to dedicate themselves to the right for any two people in love — gay or not — to walk down the matrimonial aisle.

Ten couples had initially signed up with one of the sponsors, Arlington-based Gay­Weddings.com, to renew their marriage vows surrounded by rainbow-colored roses, dainty hors d’oeuvres and a wall of balloons on the rooftop of the Embassy Hotel near Dupont Circle.

But with temperatures soaring, an hour-long shutdown of the Red Line and single-tracking until early afternoon — and only one straight couple who had arrived ready to renew their vows — organizers instead asked the crowd to join hands and vow to fight for same-sex couples’ right to marry.

“Do you promise to affirm your support for marriage equality?” intoned the officiant, Steven Gaudaen, 25, who runs a pop-up wedding company for gay and straight couples with his wife, Maggie.

“We do,” the crowd responded solemnly.

“Will you be an ally for those in need of an ally?” said the nattily dressed Gaudaen, in a suit and pink bow tie, sporting a lapel button that read “Love Kicks Ass.”

“We will,” said the crowd of about 30, many of them wedding and event planners looking not only to support marriage equality but to network in what is becoming a booming and increasingly lucrative market.

Same-sex marriage is legal in 37 states, and 6 in 10 Americans say they support it, according to a recent Washington Post-ABC News poll. The Supreme Court is considering whether the Constitution requires the states where it is not legal to issue marriage licenses to same-sex couples and, if not, whether they must recognize the marriages performed in states where same-sex marriage is legal. An affirmative ruling could, in effect, make same-sex marriage legal throughout the country.

Kate Hoffman, a spokeswoman for WeddingWire, another sponsor of the vow renewal, said the number of florists, bands, caterers and other wedding vendors who serve same-sex couples has grown from 20,000 a few years ago to 120,000. “I feel very proud that the wedding industry has always supported love,” she said.

Jennifer Johnston, of Entertainment Cruises, said that same-sex weddings make up about 40 percent of its wedding business.

“Since D.C. was one of the first places to legalize gay marriage, we really have become a destination for gay weddings,” she said, adding that the Advocate ranked the District the gayest city in the nation in 2014.

Andres Miguel Harris, a wedding photographer, said that although he is gay, he has only just begun to shoot gay weddings, and had needed to learn a whole new way of working.

“In straight weddings, everything is so bride-focused. Or you assume the bride is posed here, and the groom there,” he said. “With same-sex weddings, you want to let people pose themselves in the way they feel most comfortable. You never want to make assumptions.”

The same-sex marriage advocates also vowed to march in the Capital Pride Parade.

Last year, a military color guard marched at the head of the parade for the first time. This year, a group of Boy Scouts and Girl Scouts joined the color guard. In May, Robert M. Gates, a former defense secretary who is the president of the Boy Scouts, called on the organization to end its ban on gay leaders.

Bernie Delia, president of the Capital Pride Alliance, which organized the event, said the parade is a reflection of the growing acceptance of gay and lesbian Americans and gay rights. “We have made remarkable progress in the last 40 years,” he said.

Kathryn Hamm, publisher of GayWeddings.com and one of the sponsors of the vow renewal ceremony, said she recalled the utter terror she felt marching in the Pride Parade 25 years ago.

Though she and her wife chose not to publicly renew their private vows on the rooftop party in the morning Saturday — they were married in a civil ceremony in 1999 and threw a big wedding in 2013 — Hamm said she proudly rode on top of a convertible Mustang during the parade this year, smiling, out, open for all to see and happily, legally married.