Even his co-hosts did not know until 4 a.m. on Wednesday, just hours before the official announcement, that Matt Lauer had been fired after a serious allegation of sexual misconduct. That was when the NBC News president, Noah Oppenheim, called two of his “Today” show anchors, Savannah Guthrie and Hoda Kotb.
They would be broadcasting live to millions of viewers in three hours — and Mr. Lauer would not be joining them.
Senior executives at NBC News made the decision to fire Mr. Lauer, the face of “Today” for two decades, late Tuesday night. At 6:49 a.m., 11 minutes before airtime, Andrew Lack, the news division’s chairman, sent a memo to the staff.
In the note, he referred to “a detailed complaint from a colleague about inappropriate sexual behavior in the workplace by Matt Lauer.” Mr. Lack added that there was “reason to believe this may not have been an isolated incident.”
During a morning call with NBC News staff members, Mr. Lack said a reason for Mr. Lauer’s firing had to do with Mr. Lauer’s behavior toward a subordinate.
For NBC News, Mr. Lauer’s ignominious exit represents another setback in an already difficult period. And it has plunged morning television, a genre that depends on maintaining a mood of homey continuity, deeper into upheaval.
The move occurred a week after one of Mr. Lauer’s main competitors, Charlie Rose, the co-host of “CBS This Morning,” was fired after he faced his own spate of sexual harassment allegations.
Mr. Lauer, 59, had a greater impact on “Today” than Mr. Rose had on “CBS This Morning,” however. Inside 30 Rockefeller Plaza, Mr. Lauer was a one-man fief who wielded more behind-the-scenes influence than any other on-air personality.
With a reported annual salary of $25 million, he had the ear of top executives and a big voice in the making of “Today.” When an executive producer, Jamie Horowitz, was abruptly fired in 2014, Mr. Lauer was said to have played a role in the decision: The host was reportedly not on board with the changes that Mr. Horowitz was preparing to make.
Much of Mr. Lauer’s power stemmed from the bond he had forged with viewers as the longest tenured host in the program’s 65 years. The first two hours of “Today” — Mr. Lauer’s showcase — generated $508 million in revenue last year, more than the amount brought in by the other network morning shows, according to Kantar Media.
That windfall was $100 million more than the earnings at ABC’s “Good Morning America,” and nearly three times greater than the revenue from “CBS This Morning.” In recent months, the dollar figure was only tracking higher: Through the first half of 2017, revenue for “Today” was on the upswing once again, according to Kantar. In effect, Mr. Lauer helped subsidize a good portion of the network’s entire news operation.
Although “Good Morning America” draws a bigger overall audience than “Today,” the NBC show has beaten its ABC rival in the 25-to-54 year old age bracket important to advertisers for 100 consecutive weeks, according to Nielsen.
The termination comes toward the end of a year that was supposed to be a kind of victory lap for the host. In January, to acknowledge his 20 years on the program, “Today” aired a celebratory piece that included snippets of Mr. Lauer’s 10 interviews with presidents, nine stints as an Olympics host and reports from more than 60 countries.
“He’s like your breakfast smoothie, you know?” the former “NBC Nightly News” anchor Tom Brokaw said in the segment. “He’s kind of a high-energy drink. Easy on the palate.”
Mr. Lauer lasted so long on “Today” because he gave the impression of being equally at ease with celebrities, world leaders and the throng of sign-wielding onlookers who crowded the show’s windowed studio in Rockefeller Plaza.
All that came to an end on Tuesday night, when he joined the roster of powerful men in the media and entertainment industries — a list that includes the late Fox chairman Roger Ailes, the former Fox News Channel prime time host Bill O’Reilly, the film mogul Harvey Weinstein, the political reporter Mark Halperin and many others — who lost their positions as a result of accusations made against them by numerous women, the majority of them co-workers or job seekers.
NBC’s news division has weathered a series of contentious episodes dating back to last year’s presidential race. After a live forum of the presidential candidates in September hosted by Mr. Lauer, he received poor reviews for his handling of Hillary Clinton and Donald J. Trump, with critics arguing that he questioned Mrs. Clinton aggressively and interrupted her repeatedly while giving Mr. Trump friendlier treatment.
In October, the network was scooped by a competitor, The Washington Post, which posted the “Access Hollywood” audio recording from 2005 that captured Mr. Trump boasting to the correspondent Billy Bush about grabbing women by the genitalia and kissing them.
NBC’s failure to be first with that story in the last days of a heated campaign seemed like a strange misstep to those who watch the media closely. “Access Hollywood,” a syndicated program, is an NBC property, and the network reviewed the audio before it was leaked to The Post.
At the time when the recording was made public, Mr. Bush was working as a 9 a.m. co-host for “Today.” Two days later, NBC suspended him for his role in the lewd, off-camera conversation. The network fired him 11 days later. (Mr. Trump apologized on video for his remarks the day after they surfaced.)
Last month, NBC News once more passed on a story it could have reported first when it asked Ronan Farrow to stop reporting his expose of Mr. Weinstein. Mr. Farrow, who was a contributor for MSNBC until the network decided against renewing his contract two months ago, later published his findings in The New Yorker. Along with articles in The New York Times and other publications, Mr. Farrow’s series set off a national conversation about powerful figures and sexual misconduct.
“Today” has been described as a boys’ club in past years. Earlier this month, a booker who worked at “Today,” Matt Zimmerman, was fired after the network received allegations of inappropriate behavior with female colleagues.
Colleagues of Ann Curry, who served alongside Mr. Lauer as the co-anchor on “Today” from 2011 to 2012, said that she was undermined by male colleagues during the time after she had risen to a prominent role on the show. In an interview with People on Wednesday, Ms. Curry said, “We need to move this revolution forward and make our workplaces safe.” (She had no comment for this article.) In October, Ms. Curry was among the many women who posted the #metoo hashtag on social media to signal solidarity with the anti-sexual harassment movement.
Mr. Trump, who starred in “The Apprentice,” a long-running hit for NBC, has in the past singled out the network’s news division in his criticism of American media outlets. On Wednesday, he seized on the developments involving Mr. Lauer.
“Wow, Matt Lauer was just fired from NBC for ‘inappropriate sexual behavior in the workplace,’” Mr. Trump wrote on Twitter at 7:16 a.m. “But when will the top executives at NBC & Comcast be fired for putting out so much Fake News.”
Since his years as a New York socialite, tabloid figure and a reality star, Mr. Trump has frequently offered his opinions of television executives and producers obscure to the average viewer. In his Wednesday tweets, Mr. Trump called for the firing of two senior NBC News executives — Mr. Lack and Phil Griffin, the president of MSNBC. He also referred to an unsubstantiated conspiracy theory involving Joe Scarborough, host of “Morning Joe” on MSNBC.
“Investigate!” the president wrote at the end of his Twitter post.
The “Today” show has weathered other disruptions this year. The anchor Tamron Hall left her perch on the show’s 9 a.m. hour. She was later replaced by Megyn Kelly, the former Fox News star who accused Mr. Ailes of sexual harassment in her 2016 memoir, “Settle for More.”
Ms. Kelly’s show has gone through growing pains in its first two months on the air. In recent weeks, she has averaged a little more than two million viewers at 9 a.m., and has lost more than 20 percent of the audience that was tuning in at that hour a year ago.
ABC’s “Live with Kelly and Ryan,” with Kelly Ripa and Ryan Seacrest, regularly reaches a million more viewers each morning.
On Wednesday, after wrapping a difficult edition of their show, the stars of “Today” had a long day ahead of them. At 7 p.m., Ms. Guthrie, Ms. Kotb and Al Roker were expected to host the annual Christmas tree lighting celebration at Rockefeller Plaza.
As of Tuesday, Mr. Lauer had been scheduled to join them.