Mr. Thiel, a multibillionaire who has made his fortune as one of Silicon Valley’s top venture-capital investors, has served on the tech company’s board since 2005. He became Facebook’s first outside investor in August 2004 by acquiring a stake in the company for $500,000 that earned him hundreds of millions of dollars in profits.

Mr. Thiel decided now was the right time to leave Facebook’s board rather than be a distraction to the company ahead of the coming elections, the person said.

Meta Chairman and Chief Executive Officer

Mark Zuckerberg

said in a statement, “Peter has been a valuable member of our board and I’m deeply grateful for everything he has done for our company—from believing in us when few others would, to teaching me so many lessons about business, economics, and the world.”

Mr. Thiel is expected to step down after the company’s annual shareholder meeting, which is typically in May.

“It has been a privilege to work with one of the great entrepreneurs of our time,” Mr. Thiel said of Mr. Zuckerberg in a statement. “His talents will serve Meta well as he leads the company into a new era.”

Mr. Thiel’s departure coincides with intensifying pressures confronting Facebook on several fronts.

Meta’s stock price last week fell by 26%, shaving $323 billion from its market valuation, after the company said it expected revenue growth to slow. It also cited inflation as a weight on advertiser spending and estimated that ad-tracking changes imposed by

Apple Inc.

would cost the social-media giant $10 billion this year.

Considered the tech industry’s most prominent conservative, Mr. Thiel has long been considered one of the strongest voices on the board. He has repeatedly advised Mr. Zuckerberg not to bow to public pressure, particularly regarding the social-media network’s effects on politics.

The tech tycoon famously became Mr. Trump’s most notable ally in Silicon Valley during the 2016 election. He contributed to the Republican’s 2016 campaign and served as adviser to Mr. Trump throughout his presidency.

For the coming midterm elections, Mr. Thiel will be supporting

J.D. Vance

and

Blake Masters,

who are running for U.S. Senate seats representing Ohio and Arizona, respectively, the person said.

Mr. Masters, a Republican challenging Democratic Sen.

Mark Kelly

in Arizona, has served as chief operating officer of Thiel Capital and is president of the Thiel Foundation.

Messrs. Vance and Masters have campaigned as closely aligned with Mr. Trump on issues such as immigration and online speech. Like the former president, whose false claims of voter fraud have tested many Republicans ahead of the midterms, both Senate candidates have publicly questioned the integrity of the 2020 election, though no evidence of widespread fraud has emerged.

Messrs. Vance and Masters have also been critical of Mr. Zuckerberg’s giving more than $300 million to nonprofits that helped administer local elections, an effort they said helped to influence the 2020 election in favor of President Biden.

The Vance and Masters campaigns didn’t immediately respond to requests for comment. Facebook declined to comment.

Mr. Vance is a partner at Narya, an early-stage venture-capital fund that has invested alongside Mr. Thiel.

Mr. Thiel had discussed with people close to him the possibility of resigning from Facebook’s board as far back as 2018, after his relationship with the company came under strain following a dispute with a fellow director over Mr. Thiel’s support for Trump’s campaign.

Mr. Thiel’s politics have made him a lightning rod at Facebook, with some liberal critics citing him as a negative influence on Mr. Zuckerberg, while many conservatives see him as an essential ally in an industry that they say has long leaned to the left.

Once Mr. Thiel steps down, venture capitalist

Marc Andreessen

will be the longest-serving member of the board, which has been criticized at times as lacking independence from Mr. Zuckerberg.

As chairman and CEO, Mr. Zuckerberg controls most of the company’s voting stock through supervoting shares. The majority of Meta’s outside shareholders in recent years have voted to separate those roles, which the company has rejected.

Last month, the company appointed

DoorDash Inc.

CEO

Tony Xu

to its board of directors, adding outside executive experience to the group.

Mr. Thiel rose to prominence in the early 2000s as one of the original founders of

PayPal Holdings Inc.,

which he led as CEO until

eBay Inc.

acquired it in October 2002 for $1.5 billion. From his time at the electronic-payments platform, Mr. Thiel became one of the most visible members of the “PayPal Mafia,” a group of early employees that included Tesla Inc. CEO

Elon Musk,

who have since gone on to found and invest in other notable tech companies.

Mr. Thiel also serves as the chairman of

Palantir Technologies Inc.,

a Denver-based company that specializes in building software helping military and intelligence agencies mine and analyze data at large scales. Palantir went public in 2020 and has a market capitalization of more than $25 billion.

More recently, Mr. Thiel invested in the video-platform Rumble, which is positioning itself as a right-leaning alternative within the social-media ecosystem. Mr. Vance also invested in Rumble.

Write to Salvador Rodriguez at salvador.rodriguez@wsj.com