Mr. Ellison maneuvered Oracle ahead of Microsoft Corp. MSFT -2.95%▲ in the race to become TikTok’s U.S. tech partner, and personally lobbied President Trump to sign off on a preliminary agreement, people familiar with the talks said.

Under the current deal terms, Oracle and Walmart Inc. would take a combined 20% stake in a new U.S.-based TikTok. Oracle would guarantee the security of U.S. user information to satisfy White House concerns that China’s government might get access to such data. But the parties, including TikTok’s Beijing-based owner, ByteDance Ltd., are still finalizing their agreement and need approval from both the U.S. and Chinese governments.

Video-sharing app TikTok has come to rival some of the world’s most popular social-media platforms in just a few years. WSJ looks at how Chinese startup ByteDance took TikTok to the masses and why it attracted regulatory scrutiny. Video/illustration: Jaden Urbi/WSJ

Oracle hasn’t said what it would pay for its planned 12.5% stake, though based on estimates for TikTok’s total valuation the investment could top $7 billion. An initial public offering of TikTok in the U.S., which the preliminary deal says would happen within a year, could return some of that money.

Winning the TikTok contest would pay other dividends for Mr. Ellison, most significantly boosting Oracle’s efforts to gain traction in the hot field of cloud-computing—which he once dismissed as a fad.

As he plays catch-up with market leaders Amazon.com Inc. and Microsoft, Mr. Ellison already has deployed the hardball tactics for which he’s long been known. Oracle over the past few years has been poaching hundreds of employees from Amazon Web Services, the online retailer’s cloud arm, offering massive salary increases. And four years ago, Oracle spent around $9 billion on cloud-software provider NetSuite Inc., its biggest ever acquisition.

Oracle also has been trying to land the kind of high-profile cloud clients that bring bragging rights as well as big revenue. This year, it won business from Zoom Video Communications Inc. when the videoconferencing app needed extra capacity to handle skyrocketing demand during the pandemic.

After Mr. Trump signaled his backing for Oracle’s TikTok arrangement, the U.S. software company said in a statement its work with Zoom influenced the outcome.

This summer’s drama has also returned the billionaire back to the center of the action in the tech industry.

One of the world’s richest men, Mr. Ellison has long sought to keep Oracle in the public eye. The company paid for naming rights to the San Francisco Giants home baseball park and for the Oakland home of the National Basketball Association’s Golden State Warriors, before they moved to San Francisco. Mr. Ellison himself sits on the board of one of Silicon Valley’s buzziest companies, Tesla Inc.

But Oracle’s core business, database software for companies, is anything but splashy compared with the businesses belonging to a younger generation of tech titans such as Facebook Inc.’s Mark Zuckerberg and Amazon’s Jeff Bezos.

TikTok’s office in Culver City, Calif. Oracle has moved ahead of Microsoft in the race to become TikTok’s U.S. tech partner.

PHOTO: MIKE BLAKE/REUTERS

“Larry wants to be in the spotlight. It doesn’t matter how many billions it will cost,” said Osama Elkady, a longtime Oracle executive who left in 2013 and now is CEO at data-analytics company Incorta Inc. And Oracle, he said, has had to show it is taking the cloud seriously. “This might give them new blood,” Mr. Elkady said.

Oracle declined to make Mr. Ellison available for comment.

A college dropout, Mr. Ellison is among a small group of fabled tech entrepreneurs who drove the rise of Silicon Valley and changed how people live and do business. His competitive streak is legendary. In 2000, Mr. Ellison admitted to hiring private investigators to look into Microsoft, calling it a “civic duty.” The investigators found Microsoft helped fund companies that supported Microsoft in a battle with the Justice Department.

Mr. Ellison is an avid sports mogul who had his biggest success with the America’s Cup sailing competition. With a willingness to both spend money and tussle—he paid handsomely to lure some of Australia’s and New Zealand’s best yachtsmen—he scored a 2010 victory that returned the trophy to American hands. Mr. Ellison himself served as crew on board.

He’s also passionate about basketball. He has had a hoops court on his yacht, with a powerboat tailing it to retrieve balls that go overboard. Mr. Ellison has repeatedly tried to buy a National Basketball Association franchise, but most recently lost out on the Los Angeles Clippers to former Microsoft CEO Steve Ballmer in 2014.