Barbara Guggenheim and Alan Patricof had socialized since the 1970s. By the end of 2022, everything had changed. Shortly after signing their prenuptial agreement the morning of Dec. 7 in Miami, Barbara Guggenheim and Alan Joel Patricof were, as usual, watching the clock. Not because they were counting the days until they were married — they are so in love, both said, that this was a given — but because that’s what their lifestyles dictate.

“I think breakneck is the only speed Alan knows,” said Ms. Guggenheim, who lives in Malibu, Calif. She wasn’t exactly idle that morning either. Before the ink on the prenup was dry, several clients were awaiting her at Art Basel, the international art fair that brought her to Miami.

Ms. Guggenheim, 77, and Mr. Patricof, 89, have known each other since the early 1970s, before either had established what would become formidable reputations — Ms. Guggenheim as an art adviser to clients including Tom Cruise and Steven Spielberg, and Mr. Patricof in business.

Both were living in Manhattan when a mutual friend, the art historian Jonathan Brown, brought them together for dinners on the town. They were a party of six in those days: Ms. Guggenheim and an art dealer boyfriend, Mr. Patricof and his wife, Susan, and Mr. Brown and his wife, Sandra (Mr. Brown died in 2022).

The meet-ups were infrequent, both recall, but the company was memorable. “Alan liked new adventures,” Ms. Guggenheim said. “He was always willing to try out new restaurants. And he was lively and interested in art history or whatever the conversation was.” Mr. Patricof liked Ms. Guggenheim’s passion for art, and her hustle. “Barbara was always very knowledgeable and hardworking,” he said.

Mr. Patricof started his first firm, Alan Patricof Associates, in 1969, before “venture capital” was familiar business parlance and shorthand for how to breathe life into promising startups. That company later became Apax Partners. A second firm, Greycroft Partners, where he is still chairman emeritus, opened in 2006 and invested in companies including what was then known as the Huffington Post, Axios and Wondery. In 2020, he and a partner founded Primetime Partners, a fund that invests in goods, services and technology for people over 60. He is still the chairman there.

Bootstraps helped him conquer the corporate world. Born in New York in 1934 to immigrant parents — his mother, Dorine, was from Belarus; his father, Martin, was Ukrainian — Mr. Patricof was selling the Saturday Evening Post in the subway at age 6. “We lived a very careful life,” he said. “My parents had just enough to scrape by and educate their children,” which included his two younger sisters. “I didn’t get on a plane or ride in a taxi until the middle of college.”

At Ohio State University, he studied finance, graduating with a bachelor’s degree after three years. Two years later, he earned an M.B.A. from Columbia while working as an analyst for an investment firm.

An early marriage, in 1958, ended in divorce in 1966 after the first of his three sons, Mark, now 59, was born. In 1970, he married Susan, who became a well-known philanthropist, supporting children and global health. “My wife was brilliant and beautiful, and she was the sweetest person in the world,” he said. Ms. Patricof died of Alzheimer’s disease in January 2021; the couple had two sons, Jon, 50, and Jamie, 47.

Ms. Guggenheim, despite her familiar name, comes from a family that is entirely distinct from the one behind the Guggenheim museums and foundation. She grew up attending Quaker school in Woodbury, N.J., with a younger sister, Eileen Guggenheim Wilkinson. Their parents, Lester and Sylvia Guggenheim, owned dress shops, but Sylvia was more passionate about art than fashion.

That passion rubbed off on both girls. Ms. Guggenheim Wilkinson is chair of the board at the New York Academy of Art and a former aide to King Charles III; both sisters have doctorate degrees in art history. Before Ms. Guggenheim earned hers, from Columbia, she worked as a lecturer at the Whitney Museum of American Art to finance her way through graduate school. Her master’s degree in art history also came from Columbia. Her bachelor’s degree in art history is from Douglass College at Rutgers University.

“I’ve seen the art world from different angles,” she said, including as the entrepreneur behind the ’70s-era Art Tours of Manhattan, which brought visitors to art studios and galleries, and as the head of the American Painting Department at the auction house Christie’s.

In 1981, she founded an art advisory company that morphed into Guggenheim, Asher Associates. She is still president there. She didn’t marry Bert Fields, an entertainment lawyer known for representing Hollywood film studios and clients including George Lucas, Michael Jackson, Warren Beatty and Dustin Hoffman, until 1991, when she was in her early 40s.

The couple had no children but several homes. “I collect houses, not art,” said Ms. Guggenheim, who owns four but considers Malibu her primary residence. “I don’t want to compete with my clients.”

Like Mr. Patricof’s, her marriage was enduring. When Mr. Fields died last year of complications from long Covid, Mr. Patricof went to the memorial in Los Angeles. And because the couples had socialized throughout the years, Ms. Guggenheim, likewise, mourned with Mr. Patricof when Susan, whom she had long admired, died.

“We both had great marriages,” Mr. Patricof said. Their decision this fall to start a new one together surprised them more than it surprised friends.

They’re as well matched energetically as they are socially, he said. Mr. Patricof runs marathons — last year, he was the oldest person to complete the New York City Marathon — and Ms. Guggenheim is a competitive ballroom dancer. Both write books in their spare time. Mr. Patricof’s “No Red Lights: Reflections on Life, 50 Years in Venture Capital and Never Driving Alone,” published by Post Hill Press, came out last year; Ms. Guggenheim has written five books on art, including “Art World: The New Rules of the Game,” published by Marmont Lane in 2017, and is working on a collection of stories.

Neither would call the courtship traditional. In 2020, when Ms. Patricof’s disease had progressed so much she was confined to the couple’s Upper East Side apartment, Mr. Patricof often found himself in need of a partner for social obligations. “I told my children and my friends, don’t be surprised if you see me out with someone,” he said. “Barbara and I were both unbelievably dedicated to our marriages. But it’s tough to be alone.”

Ms. Guggenheim, on the West Coast, was too far away to be in his lineup of possible companions. She was also busy caring for Mr. Fields, whose health was declining. But she helped in another way. “Alan would need a plus-one, and I would vet them,” she said. By 2022, she was noticing a shift in how she felt about her vetting duties.

When visiting New York, “I would go places with him, and if we ran into someone he had gone out with or was going to go out with, I felt a little pang of jealousy,” she said. Both went on a few blind dates after their spouses died, but by the end of 2022, “I think we both came to the conclusion that we’d rather be with each other than with anyone else,” she added.

Both reject the idea that their romance was built on convenience. “It’s nice to be with someone who fits in with your friends and your family,” Mr. Patricof said. “But it’s as simple as, we fell in love. We have a love affair now.” As Ms. Guggenheim put it, “I always laugh, because people probably think we’re two old losers who just decided, let’s glue it together. It’s not like that.”

The relationship glue known as marriage hadn’t occurred to either when they were at a cocktail party in September in the Hamptons and a friend congratulated them on their engagement. “He mentioned the name of a mutual friend who had told him we were getting married,” Mr. Patricof said. The friend had started the rumor — neither knows why, but both found it amusing. A few days later, they took a long walk in East Hampton. “I said, ‘Since he said it, why don’t we do it?’”

Among the things Ms. Guggenheim loves about Mr. Patricof, she said, is that he’s game. That day, she was game. She said yes.

On Dec. 10, they were married in the Park Avenue apartment Mr. Patricof has lived in since 1970. Just 40 family members and a few close friends had been invited.

David Gelfand, the rabbi at Temple Israel of the City of New York, officiated a traditional Jewish ceremony. Before each stomped a glass to mark the start of their marriage, Rabbi Gelfand told guests the wedding was life affirming. “People their age are typically going to funerals,” he said. Not them.

Mr. Patricof often tells people he expects to live to 114. “I promised Barbara we’d have 25 years together,” he said. She’s counting on it. “Alan is irresistible,” she said.

On This Day

When Dec. 10, 2023

Where Park Avenue, New York

Recycled Rings During the ceremony, the couple exchanged rings. But not new ones. Each gave the other the band they had worn in their previous marriages. “Our marriages were both long and good,” Ms. Guggenheim said. “We figured it was a good omen.”

Something Spectacular Ms. Guggenheim turned 77 on her wedding day. During a reception in the apartment, while guests sipped bellinis and mimosas and helped themselves to a buffet of lox and bagels, a bouquet of flowers arrived. “In the middle of everything, I got birthday flowers from Tom Cruise,” she said. It was not a small bouquet. “He does nothing that’s not spectacular.”

And Something Signature For her short walk down the living room aisle, she carried a lily of the valley bouquet — her mother’s favorite flower — and wore a white Dior pantsuit she pulled from her closet. Mr. Patricof wore his signature outfit, a blue suit from J. Crew.

Collection Intact Ms. Guggenheim will move to New York in the new year, though she will hang onto her other properties, including the Malibu home.