Sheryl Sandberg, the chief operating officer of Meta and the longtime second in command to its founder, Mark Zuckerberg, said on Wednesday that she was stepping down after 14 years, as the company continues facing questions about its social media platform and as it navigates a transition to the so-called metaverse.

Ms. Sandberg, 52, said she was leaving Meta — which owns Facebook, Instagram, WhatsApp and other apps — this fall and that she planned to continue serving on the company’s board of directors. In an interview, she said that joining Facebook was the “honor and privilege of a lifetime,” and that she initially expected to do it for roughly five years rather than the 14 she has served.

Ms. Sandberg said the job did not leave her with time for many other pursuits and that she now wished to focus on her personal philanthropy and her foundation, Lean In. She is also set to be married this summer, to Tom Bernthal, a television producer.

“I believe in this company,” Ms. Sandberg said in the interview. “Have we gotten everything right? Absolutely not. Have we learned and listened and grown and invested where we need to? This team has and will.”

Mr. Zuckerberg named Javier Olivan, a longtime product executive, as Meta’s next chief operating officer. Mr. Olivan has overseen much of Facebook’s growth over the past decade, and has managed WhatsApp, Instagram, Messenger and Facebook.

Ms. Sandberg is ending her tenure at Meta far from the reputational pinnacle she had reached last decade. As a key lieutenant to Mr. Zuckerberg, Ms. Sandberg helped build up Facebook’s business in the company’s early years and was regarded as the adult in the room. Facebook’s advertising business flourished under her, and Ms. Sandberg used her corporate fame to speak up on other issues, such as what women could achieve in the workplace.

But after the 2016 presidential election, Facebook came under intense scrutiny for how it was misused to stoke division and to spread misinformation. Ms. Sandberg was responsible for the policy and security team at the company during that election. The social network also was dogged by privacy questions after a scandal involving Cambridge Analytica, a voter-profiling firm that improperly used Facebook data.

Ms. Sandberg, who was one of Facebook’s most visible executives, was unable to recover from those stumbles. In recent years, Mr. Zuckerberg took a higher public profile and a greater role in overseeing different parts of the company, many of which had been under Ms. Sandberg’s sole purview.

Her departure also comes as Facebook is moving in a new direction. Last year, Mr. Zuckerberg renamed the company Meta and announced it would become a key provider of the metaverse, an immersive online world. But as the company has been spending heavily on metaverse products, its advertising business has stumbled, partly because of privacy changes made by Apple that have hurt targeted advertising.

In February, Meta’s market value plunged by more than $230 billion, its biggest one-day wipeout after it reported financial results that showed it was struggling to make the leap to the metaverse.

In the interview, Ms. Sandberg said Meta faced near-term challenges but would weather the storm as it had during past challenges. “When we went public, we had no mobile ads,” Ms. Sandberg said, citing the company’s rapid transition from desktop to smartphones last decade. “We have done this before.”

Ms. Sandberg has flirted with leaving Facebook in the past. In 2016, she told colleagues that if Hillary Clinton, the Democratic presidential nominee, won the White House she would most likely assume a job in Washington, three people who spoke to her about the move at the time said. In 2018, after revelations about Cambridge Analytica and Russia’s interference in the 2016 U.S. presidential election, she again told colleagues that she was considering leaving but did not want to do so when they were in crisis.

In a Facebook post on Wednesday, Mr. Zuckerberg praised Ms. Sandberg.

“It’s unusual for a business partnership like ours to last so long,” he wrote. “Sheryl architected our ads business, hired great people, forged our management culture, and taught me how to run a company.”

This is a developing story. Check back for updates.