CNN called it first, at 11:24 a.m. on Saturday, quickly followed by NBC, CBS, ABC and The Associated Press. Fox News waited until 11:40 a.m.
The projection that Joseph R. Biden Jr. would become the 46th president of the United States came after days of slow-burning suspense on the cable news networks and broadcast channels. As millions of anxious viewers watched, the anchors and pundits filled hours of airtime by tracking the vote counts in battleground states. All the while, President Trump fumed and filed legal challenges in the background of the incremental ballot-count developments in Nevada, Georgia, Pennsylvania and Arizona.
Going into Saturday, Fox News and The Associated Press were in a position to make the declaration for Mr. Biden before any other news organization: They were alone in projecting that Mr. Biden had won the Arizona vote, with Fox News making the call at 11:20 p.m. on Tuesday and The A.P. following hours later. Because of those calls, Fox News and The A.P. had Mr. Biden with 264 electoral votes, six shy of the 270 necessary for a White House victory. Other news organizations had Mr. Biden at 253 electoral votes early on Saturday.
But Fox News and The A.P., which had come in for criticism by Mr. Trump and some data journalists for possibly jumping the gun on Arizona, held back on Saturday, playing it safe and waiting until the other major media organizations made the call.
“The Fox News decision desk can now project that former Vice President Joe Biden will win Pennsylvania and Nevada, putting him over the 270 electoral votes he needs to become the 46th president of the United States,” the Fox News anchor Bret Baier told viewers at 11:40 a.m.
Before the arrival of Mr. Baier and Martha MacCallum at the Fox News anchor desk on Saturday, Neil Cavuto had been on the air while other news outlets made the call.
“After four long tense days, we’ve reached a historic moment in this election,” Wolf Blitzer, of CNN, announced. “We can now project the winner of the presidential race: CNN projects Joseph R. Biden is elected the 46th president of the United States, winning the White House and denying President Trump a second term. We’re able to make this projection because CNN projects Biden wins Pennsylvania.”
CNN’s call came after a batch of about 3,000 votes of votes had come in from Philadelphia, heavily skewed in Mr. Biden’s favor. Throughout the morning, CNN had indicated a call could be coming.
Moments afterward, the CNN correspondent Abby Phillip noted, referring to Mr. Biden, that it was “a white old man who did it.” Ms. Phillip added, “It is a cathartic moment for millions and millions of Americans.”
The anchor Anderson Cooper asked the pundit Van Jones for his reaction. Mr. Jones, tearing up behind his eyeglasses, took a moment before saying, “Well, it’s easier to be a parent this morning. It’s easier to be a dad. It’s easier to tell your kids that character matters.”
On Fox News, Mr. Baier said, speaking of Mr. Trump after the news had been reported, “We have to remember that he is the president until Jan. 20. And there are interesting things that could or could not happen during that time while these legal challenges are going on.”
The anchor Chris Wallace noted that Mr. Trump “is going to end up with more votes than anybody in history — except for Joe Biden this year,” adding, “He is going to be a big player. He is not going to go away and be quiet.”
But Mr. Wallace seemed unimpressed with the president’s talk of a fraudulent election and his legal challenges. “I think it’s going to become increasingly untenable,” he said. He noted that Senator Lindsey Graham, Republican of South Carolina, had begun to talk of a Biden presidency and predicted that his Republican colleagues in the House and Senate would follow his lead.
Shortly after 12:30 p.m., Fox News broadcast scenes of revelers in the streets of Lansing, Mich., Washington, D.C., and New York City, as well as a group of Trump supporters in Harrisburg, Pa., who were waving Trump flags and carrying signs that said, “Stop the Steal,” a reference to the president’s unfounded claims that the election was fraudulent.
Edmund Lee and Katie Robertson contributed reporting.