Peter Thiel, one of the longest-serving board members of Meta, the parent of Facebook, plans to step down, the company said on Monday.

Mr. Thiel, 54, wants to focus on influencing November’s midterm elections, said a person with knowledge of Mr. Thiel’s thinking who declined to be identified. Mr. Thiel sees the midterms as crucial to changing the direction of the country, this person said, and he is backing candidates who support the agenda of former president Donald J. Trump.

Over the last year, Mr. Thiel, who has a net worth estimated at $2.6 billion by Forbes, has become one of the Republican’s Party’s largest donors. He gave $10 million each last year to the campaigns of two protégés, Blake Masters, who is running for a Senate seat in Arizona, and J.D. Vance, who is running for Senate in Ohio.

Mr. Thiel has been on Meta’s board since 2005, when Facebook was a tiny start-up and he was one of its first institutional investors. But scrutiny of Mr. Thiel’s position on the board has steadily increased as the company was embroiled in political controversies, including barring Mr. Trump from the platform, and as the venture capitalist has become more politically active.

The departure means Meta loses its board’s most prominent conservative voice. The 10-member board has undergone significant changes in recent years, as many of its members have left and been replaced, often with Silicon Valley entrepreneurs. Drew Houston, the chief executive of Dropbox, joined Facebook’s board in 2020 and Tony Xu, the founder of DoorDash, joined it last month. Meta didn’t address whether it intends to replace Mr. Thiel.

The company, which recently marked its 18th birthday, is undertaking a shift toward the so-called metaverse, which Mr. Zuckerberg believes is the next generation of the internet. Last week, Meta reported spending more than $10 billion on the effort in 2021, along with mixed financial results. That wiped more than $230 billion off the company’s market value.

“Peter has been a valuable member of our board and I’m deeply grateful for everything he’s done for our company,” Mark Zuckerberg, chief executive of Meta, said in a statement. “Peter is truly an original thinker who you can bring your hardest problems and get unique suggestions.”

In a statement on Monday, Mr. Thiel said: “It has been a privilege to work with one of the great entrepreneurs of our time. Mark Zuckerberg’s intelligence, energy and conscientiousness are tremendous. His talents will serve Meta well as he leads the company into a new era.”

Mr. Thiel first met Mr. Zuckerberg 18 years ago when he provided the entrepreneur with $500,000 in capital for Facebook, valuing the company at $4.9 million. That gave Mr. Thiel, who with his venture firm Founders Fund controlled a 10 percent stake in the social network, a seat on its board of directors.

Since then, Mr. Thiel has become a confidante of Mr. Zuckerberg. He counseled the company through its early years of rapid user growth, and through its difficulties shifting its business to mobile phones around the time of its 2012 initial public offering.

He has also been seen as the contrarian who has Mr. Zuckerberg’s ear, championing unfettered speech across digital platforms when it suited him. His conservative views also gave Facebook’s board what Mr. Zuckerberg saw as ideological diversity.

In 2019 and 2020, as Facebook grappled with how to deal with political speech and claims made in political advertising, Mr. Thiel urged Mr. Zuckerberg to withstand the public pressure to take down those ads, even as other executives and board members thought the company should change its position. Mr. Zuckerberg sided with Mr. Thiel.

But Mr. Thiel’s views on speech were at times contradictory. He funded a secret war against the media website Gawker, eventually resulting in the site’s bankruptcy.

Mr. Thiel’s political influence and ties to key Republicans and conservatives have also offered a crucial gateway into Washington for Mr. Zuckerberg, especially during the Trump administration. In October 2019, Mr. Zuckerberg and Mr. Thiel had a private dinner with President Trump.

Facebook and Mr. Zuckerberg have long taken heat for Mr. Thiel’s presence on the board. In 2016, Mr. Thiel was one of the few tech titans in largely liberal Silicon Valley to publicly support Mr. Trump’s presidential campaign.

In 2020, when Mr. Trump’s incendiary Facebook posts were put under the microscope, critics cited Mr. Thiel’s board seat as a reason for Mr. Zuckerberg’s continued insistence that Mr. Trump’s posts be left standing.

Facebook banned Mr. Trump’s account last year after the Jan. 6 storming of the U.S. Capitol, saying his messages incited violence. The episode became a key rallying point for conservatives who say that mainstream social platforms have censored them.

Mr. Vance, who used to work at one of Mr. Thiel’s venture funds, and Mr. Masters, the chief operating officer of Mr. Thiel’s family office, have railed against Facebook. In October, the two Senate candidates argued in an opinion piece in The New York Post that Mr. Zuckerberg’s $400 million in donations to local election offices in 2020 amounted to “election meddling” that should be investigated.

Recently, Mr. Thiel has publicly voiced his disagreement with content moderation decisions at Facebook and other major social media platforms. In October at a Miami event organized by a conservative technology association, he said that he would “take QAnon and Pizzagate conspiracy theories any day over a Ministry of Truth.”

Mr. Thiel’s investing has also clashed with his membership on Meta’s board. He invested in the company that became Clearview AI, a facial-recognition start-up that scraped billions of photos from Facebook, Instagram and other social platforms in violation of their terms of service. Founders Fund also invested in Boldend, a cyberweapons company that claimed it had found a way to hack WhatsApp, the Meta-owned messaging platform.

Meta declined to comment on Mr. Thiel’s investments.

In the past year, Mr. Thiel, who also is chairman of the software company Palantir, has increased his political giving to Republican candidates. Ahead of the midterms, he is backing three Senate candidates and 12 House candidates. Among those House candidates are three people running primary challenges to Republicans who voted in favor of impeaching Mr. Trump for the events of Jan. 6.