WINDSOR, England

Prince Harry and his American actress bride Meghan Markle married on Saturday in a dazzling ceremony that blended ancient English ritual with African-American culture, infusing the 1,000-year-old British monarchy with a blast of blackness and modernity.

It was a wedding to remember — and to tweet about — as celebrity guests and royals filled the medieval St. George’s Chapel at Windsor Castle that 39 English kings and queens have called home since 1066.

With regal pageantry as abundant as the garlands of flowers, Prince Harry and Ms. Markle exchanged vows in a ceremony watched by a global television audience of millions.

Alighting from a vintage Rolls-Royce Phantom IV at the chapel, Ms. Markle was stunning in an ivory silk, A-line Givenchy gown designed by Clare Waight Keller with a bateau neckline and three-quarter sleeves, diamond tiara and 16 ½-foot silk tulle veil hand-embroidered with flora representing the 53 countries of the British Commonwealth.

Two pageboys, the 7-year-old twin sons of her best friend Jessica Mulroney and Benedict Mulroney, the son of former Canadian Prime Minister Brian Mulroney, followed Ms. Markle, carrying her veil up the steps of St. George’s Chapel.

She entered the chapel unescorted, and was met halfway down the aisle by Prince Harry’s father, Prince Charles, who walked her to the altar before she and the groom exchanged vows and were proclaimed husband and wife.

Ms. Markle’s father, Thomas Markle, 73, a former lighting director for TV soaps and sitcoms who lives reclusively in Rosarito, Mexico, pulled out of the ceremony earlier in the week, telling TMZ that he had heart surgery on May 16.

The union of Prince Harry, 33, a former royal wild child and sixth in line to the British throne, and 36-year-old Ms. Markle, a divorcee whose mother is African-American and father is white, was like no other the royal family has seen before.

“We can break the barriers down, it can be done,” said 40-year-old black Briton Yvonne Emanuel, one of the 100,000-strong crowd that thronged Windsor’s streets.

The ceremony was typical of royal weddings in many ways. The service was conducted by the Dean of Windsor, while Justin Welby, the Archbishop of Canterbury, declared the couple man and wife, beneath the banners of the knights of the Order of the Garter, the world’s oldest chivalric group dating back to 1348.

But throughout the wedding, there were significant breaks with tradition, in particular when Bishop Michael Bruce Curry, head of the Episcopal Church in the United States, delivered a passionate sermon that was a far cry from the sober tones of the Church of England.

“There’s power in love,” Bishop Curry boomed at a congregation that included Queen Elizabeth, senior royals and celebrities ranging from Oprah Winfrey to tennis star Serena Williams and husband Alexis Ohanian, George and Amal Clooney and soccer star David Beckham.

“Do not underestimate it. Anyone who has ever fallen in love knows what I mean,” he said in an energetic, 16-minute address that quoted Dr. Martin Luther King Jr., cited spirituals, medieval poetry, the Bible and experiences of enslaved people in the American South.

He said that love was not just for young couples, but part of God’s plan with the power to change the world.

“We will let justice roll down like a mighty stream and righteousness like an ever-flowing brook,” he said. “When love is the way, poverty will become history. …We would treat one another as family.”

The Chicago native and former bishop of North Carolina grasped the lecturn at times, and at other times waved his arms to punctuate points. His sermon was the most tweeted moment of the royal wedding.

“It was a moment for African-Americans,” said Karen Long, who came from Houston, Texas, with her sister and a group of friends, all dressed as bridesmaids, to listen to the wedding from loudspeakers placed around Windsor.

“The idea that Harry allowed that and acknowledged it, it was the perfect blend between her culture and the royal culture.”

While members of the royal family, including Prince Harry’s brother, Prince William, could be seen smiling during the sermon, Ms. Markle’s mother, Doria Ragland, 61, nodded several times as Bishop Curry spoke. Ms. Ragland also shed a few tears during the ceremony.

As well as traditional Church of England anthems and delicate English choral music, the ceremony also featured a gospel choir, The Kingdom Choir directed by Karen Gibson, singing “Stand by Me,” the 1960s hit by American singer Ben E. King.

Prince Harry reportedly suggested a gospel element be added.

Cellist Sheku Kanneh-Mason of Nottingham, a 19-year-old winner of a BBC competition, played three selections during the ceremony, captivating the congregation and television viewers around the world.

In further breaks with tradition, Ms. Markle did not vow to obey her husband. The couple also exchanged rings, meaning that, unlike other senior male royals such as his older brother Prince William, Prince Harry will wear a wedding band.

At the ceremony’s end, the couple, now officially known as the Duke and Duchess of Sussex — titles bestowed by Queen Elizabeth — kissed on the steps of the chapel, before a delighted sea of well-wishers. The couple got into a horse-drawn carriage and toured Windsor, waving to vast crowds of people, some of whom had camped for days to witness the spectacular show of British pomp and pageantry.

The enthusiasm from the crowds waving and cheering was overwhelming. Thousands more celebrated at street parties held across Britain and around the globe.

Ishea Brown held a “Black A.F. Royal Wedding Brunch” in Seattle attended by more than a dozen of her friends. Not a longtime devotee of all things royal, Ms. Brown said he was not particularly interested in the House of Windsor until November, when the wedding was announced.

“These are things that growing up I never would have thought we would see,” said Ms. Brown, 33, referring to a woman with African-American heritage becoming a member of the royal family. “I hope that women, but particularly black women, are able to see themselves in her and her mother, and know that there are no spaces that are not meant for us.”

Also among the celebrities at the nuptials were actor Idris Elba and his fiancée, Sabrina Dowhre and Sir Elton John, who sang at the funeral of Prince Harry’s mother, Princess Diana, in 1997. He also performed at Prince Harry and Ms. Markle’s wedding reception, held in the castle’s St George’s Hall.

The royal couple, who met on a blind date in 2016 and fell in love in a tent under the stars in Botswana, later left for an after-party in a silver blue Jaguar E-Type for nearby Frogmore House mansion. Ms. Markle, wearing her second gown of the day, a sleek, long white dress designed by Stella McCartney, made a speech at the evening event, another break with tradition, to which about 200 guests were invited.

After watching the ceremony from California, Mr. Markle told TMZ it had been “emotional and joyful.”

“My baby looks beautiful and she looks very happy. I wish I were there and I wish them all my love and all happiness.”

The newlyweds did not immediately leave for a honeymoon. Instead, they appeared at their first official engagement since becoming husband and wife when they attended an event Tuesday in the gardens of Buckingham Palace celebrating Prince Charles’ charity patronages and military affiliations ahead of his 70th birthday in November.

The couple is expected to go on a honeymoon later, although no details of when or where have been announced.