Facebook wanted Mr. Clegg to help repair its relationships with regulators, political leaders and the media after the Cambridge Analytica scandal, when data improperly pulled from Facebook was used by to create voter profiles. Mr. Clegg’s international experience and comfort in five languages — English, Spanish, French, German and Dutch — appealed to the American-centric company.

Friends said Mr. Clegg had initially been reluctant to join Facebook, one of the world’s most polarizing corporations. But he wanted to be back at the center of important political and policy debates. In a memo outlining how he envisioned the role, he argued that it was unsustainable for a private company like Facebook, rather than democratically elected governments, to have so much power, especially on speech-related issues.

“My advice was strongly to go for it,” said Tony Blair, the former British prime minister, whom Mr. Clegg spoke with before taking the job, “because you’re going to be part of one of the most powerful companies in the world at a moment of enormous change in the world, and when technology is at the heart of that change.”

Inside Facebook, where Mr. Zuckerberg leans on a group of friends and early employees for counsel, Mr. Clegg earned the trust of his new boss. At the company’s headquarters, where proximity to Mr. Zuckerberg is power, Mr. Clegg’s desk was placed nearby. He orchestrated a trip through Europe with Mr. Zuckerberg, meeting with European Union leaders in Brussels and President Emmanuel Macron of France in Paris.

Since Mr. Clegg’s arrival, Facebook has shifted some of its policy positions. It now appears more accepting of regulation and higher taxes. He overcame reluctance from Mr. Zuckerberg and others in the company to ban political ads in the weeks before Election Day last year. And he was the main internal supporter for recently announced product changes that give users more control over what posts they see in their Facebook feeds.

“He has a track record of knowing what it’s like to work inside a cabinet that needs to make decisions quickly and move at the speed of a country, or in this case a platform,” said Chris Cox, Facebook’s chief product officer, who worked with Mr. Clegg on the user-control changes.