The New York Times Company has reached an agreement to buy The Athletic, the online sports news outlet with 1.2 million subscriptions, in an all-cash deal valued at $550 million, The Times said on Thursday.

The deal brings The Times, which has more than eight million total subscriptions, quickly closer to its goal of having 10 million subscriptions by 2025, while also offering its audience more in-depth coverage of the more than 200 professional teams in North America, Britain and Europe that are closely followed by The Athletic’s journalists.

Meredith Kopit Levien, the chief executive of the Times Company, called The Athletic “a great complement to The Times.”

“We are now in pursuit of a goal meaningfully larger than 10 million subscriptions and believe The Athletic will enable us to expand our addressable market of potential subscribers,” she said.

Under Times ownership, The Athletic will be operated separately from The Times’s newsroom and its sports section, the company said. The publisher will be David Perpich, a longtime senior executive at The Times who has been a leader of its Cooking and Games apps, as well as the product recommendation site Wirecutter.

Alex Mather and Adam Hansmann, who started The Athletic in 2016, will stay on after the acquisition. Mr. Mather, currently the site’s chief executive, will become general manager and co-president; Mr. Hansmann, now The Athletic’s president, will be its chief operating officer and co-president.

“We started The Athletic to bring fans closer to the teams, players and leagues they love through deep, immersive journalism and storytelling,” Mr. Mather and Mr. Hansmann said in a statement on Thursday. “Today marks a thrilling milestone for that dream, one realized because of the hard work of every single one of our employees. We are proud to have The Athletic become part of the Times Company’s family of subscription products.”

Mr. Mather and Mr. Hansmann, formerly colleagues at the fitness tracking app Strava, started The Athletic in the belief that die-hard fans were not finding the coverage they craved at a time when newspapers were in decline, Sports Illustrated was undergoing an ownership change and ESPN began laying off journalists.

They hired prominent sports journalists from across the country and expanded quickly, bringing coverage of games and the latest sports developments to readers who had grown accustomed to getting news online. The Athletic had a reporter covering nearly every major professional sports team in North America, as well as several top European soccer clubs, while also serving up magazine-length feature articles and podcasts.

The site has about 600 employees — roughly 400 in its newsroom, making it the second-largest employer of sports journalists in the country, behind the Disney-owned ESPN. Like a number of digital media companies that have found success in recent years, The Athletic relies on subscribers, rather than advertisers, as its main source of revenue.

Recently, as its rapid subscription growth began to slow, The Athletic explored various options, including selling a minority or majority stake in the company, with private equity firms and corporations as potential buyers.

The Times’s acquisition of The Athletic is expected to close in the first quarter of 2022. For The Times, the addition will bring an infusion of paying readers. Ms. Levien has consistently emphasized the importance of adding digital subscribers since taking charge of the business in 2020. At the end of the third quarter of 2021, the Times Company had reached 8.4 million total subscriptions.

The Times’s growth in recent years has included other big-ticket acquisitions. In 2016, the Times Company bought The Wirecutter and its sibling site, The Sweethome, for more than $30 million. In 2020, The Times bought Serial Productions, the company behind the “Serial” podcast, for more than $25 million. The same year, it acquired Audm, an app that offers listeners articles read aloud.

When Mr. Mather and Mr. Hansmann started The Athletic, they said much of the nation’s sports coverage was “empty calories” produced by slowly dying newspapers, adding that a media company focused on journalism for sports fans would be better for readers.

Early on, Mr. Mather boasted in an interview with The Times that The Athletic’s goal was to let local newspapers “continuously bleed until we are the last ones standing.”

Katie Robertson contributed reporting.