On Wednesday, a Facebook-appointed panel of journalists, activists, and lawyers ruled to uphold the social network’s ban on former President Donald J. Trump, effectively ending Mr. Trump’s immediate return to mainstream social media and reigniting a debate about tech power over online speech.

The Oversight Board of Facebook, which acts as a quasi-court over the company’s content decisions, ruled that the social network was correct to bar Mr. Trump after he used the site to incite an insurgency in Washington in January. The panel determined that the ongoing threat of violence “justified” the suspension.

However, the board also stated that an indefinite suspension was “not appropriate” and that the company should impose a “defined penalty.” Facebook was given six months to make a final decision on Mr. Trump’s account status, according to the board.

The decision complicates Mr. Trump’s return to mainstream social media, which he used during his presidency to cajole, set policy, criticize opponents, and enrage his tens of millions of followers. Twitter and YouTube had also cut off Mr. Trump in January following the Capitol building insurgency, citing the risk of harm and the potential for violence that he had created.

While Mr. Trump’s Facebook account is currently suspended, he may be able to rejoin the social network once the company reviews its action. Mr. Trump unveiled a new website, “From the Desk of Donald J. Trump,” on Tuesday to communicate with his supporters. It resembled a Twitter feed, complete with posts written by Mr. Trump and shareable on Facebook, Twitter, and YouTube.

Mr. Trump’s continued suspension of Facebook provided new ammunition to conservatives who have long accused social media platforms of suppressing right-wing voices. Facebook CEO Mark Zuckerberg has testified in Congress several times in recent years about whether the social network has a bias against conservative political views. He has flatly denied it.

Democrats took aim at how Facebook can be used to disseminate false information. “Donald Trump has played a big role in helping Facebook spread disinformation, but whether he’s on the platform or not, Facebook and other social media platforms with the same business model will find ways to highlight divisive content to drive advertising revenues,” said Frank Pallone, chairman of the House Energy and Commerce Committee.

Facebook said in a statement that it was “pleased” that the board recognized that its decision to bar Mr. Trump in January was justified. The company also stated that it would consider the ruling and “determine a clear and proportionate action.”

Mr. Trump’s case is the most high-profile that the Facebook Oversight Board, which was established in 2018, has dealt with. The board, which consists of 20 journalists, activists, and former politicians, reviews and decides on the company’s most contentious content moderation decisions. Mr. Zuckerberg has referred to it as the “Facebook Supreme Court” on numerous occasions.

However, despite the panel’s claim to independence, it was founded and funded by Facebook and has no legal or enforcement authority. Critics have questioned the board’s autonomy, claiming it gives Facebook the ability to postpone difficult decisions.

Each case is decided by a five-member panel chosen from among the board’s 20 members, one of whom must be from the country where the case originated. The panel considers the case comments and makes recommendations to the full board, which decides by majority vote. Facebook has seven days after a ruling to act on the board’s decision.

Since beginning to issue rulings in January, the board has overturned Facebook’s decisions in four of the five cases it has reviewed. In one case, the board asked Facebook to restore a post that used Nazi propaganda chief Joseph Goebbels to make a point about Trump’s presidency. Facebook had previously removed the post because it “promoted dangerous individuals,” but had now agreed to the board’s decision.

In Mr. Trump’s case, Facebook also asked the board to make recommendations on how to handle political leaders’ accounts. On Wednesday, the board suggested that the company should publicly explain when it applied special rules to influential figures, but that it should do so within a specific time frame. The board also stated that Facebook should clarify its strikes and penalties process, as well as develop and publish a policy that governs responses to crises or novel situations in which its regular processes would not prevent imminent harm.