Also, former "Prairie Home Companion" host Garrison Keillor was cut loose by Minnesota Public Radio over an allegation of "inappropriate behavior." Keillor, 75, said he inadvertently put his hand on a woman's bare back in an attempt to console her.
Lauer has long been one of the most-liked and highest-paid figures in the TV news industry, and his fall startled many of the roughly 4 million viewers who start their day with the NBC News show.
Network news chief Andrew Lack said in a memo to the staff that NBC received a complaint about Lauer's behavior on Monday and determined it violated company standards. NBC said the misconduct started when Lauer and a network employee were at the Sochi Olympics in 2014 and continued beyond that assignment.
Lack said it was the first complaint ever lodged against Lauer, but "we were also presented with reason to believe this may not have been an isolated incident."
However, Variety later documented multiple accounts of Lauer's behavior at NBC as part of a two-month investigation by the magazine that included dozens of interviews with current and former staffers. Variety reported talking to three women who identified themselves as victims of sexual harassment by Lauer.
Lauer becomes the second morning host in a week to lose his job over sexual misconduct allegations. CBS fired Charlie Rose after several women who worked for him complained about his behavior.
Messages to Lauer and his agent were not immediately returned, and the network would not say whether he denied or admitted to any wrongdoing. He is married with three children.
Matt Lauer has been terminated from NBC News. On Monday night, we received a detailed complaint from a colleague about inappropriate sexual behavior in the workplace by Matt Lauer. As a result, we’ve decided to terminate his employment. pic.twitter.com/1A3UAZpvPb— TODAY (@TODAYshow) November 29, 2017
Lauer, 59, has essentially been the king of television morning news since first being paired with Katie Couric on "Today" in 1997.
For many years, "Today" was the unquestioned ratings leader, until it was eclipsed by ABC's "Good Morning America" following the ugly 2012 firing of Lauer's co-host Ann Curry. The show had stabilized in recent years with Lauer's pairing with Savannah Guthrie.
Lauer's "Where in the world is Matt Lauer?" segments were popular for years, and he was used by NBC for other events. He had been scheduled to host the network's coverage of the Rockefeller Center Christmas tree lighting ceremony Wednesday evening.
He joins a lengthening list of media figures felled by sexual misconduct accusations this year. Besides Rose, they include Lauer's NBC News colleague Mark Halperin, Fox News prime-time host Bill O'Reilly and National Public Radio newsroom chief Michael Oreskes. The New York Times suspended White House correspondent Glenn Thrush last week.
The flood of allegations was set off in large part by the downfall of Hollywood studio boss Harvey Weinstein, who has been accused of sexually assaulting or harassing numerous women.
Ari Wilkenfeld, the attorney for Lauer's accuser, praised NBC for acting "quickly and responsibly" in response to the morning host's "egregious acts of sexual harassment and misconduct." The lawyer did not identify his client.
Lack, in his memo, said, "We are deeply saddened by this turn of events. But we will face it together as a news organization - and do it in as transparent a manner as we can."
An immediate challenge is filling a giant hole on a show that has long been the most lucrative for NBC News. One potential replacement, Willie Geist, on Wednesday called Lauer someone "I have always looked up to in the business, and he taught me a lot."
As for Keillor, Minnesota Public Radio said it will end distribution of the radio program "The Writer's Almanac," Keillor's daily reading of a poem and telling of literary events, and end rebroadcasts of old "Prairie Home Companion" episodes.
"I meant to pat her back after she told me about her unhappiness and her shirt was open and my hand went up it about six inches. She recoiled. I apologized. I sent her an email of apology later and she replied that she had forgiven me and not to think about it," Keillor said in an email to the Minneapolis Star Tribune. "We were friends. We continued to be friendly right up until her lawyer called."
At NBC, Lauer's former "Today" colleagues, Guthrie and Hoda Kotb, announced the firing on the show Wednesday morning shortly after being told themselves.
Guthrie appeared to fight back tears as she called Lauer her friend who is beloved by many at NBC, and said she was "heartbroken for my colleague who came forward to tell her story and any other women who have their own stories to tell."
"How do you reconcile your love for someone with the revelation that they have behaved badly? I don't know the answer to that," she said. "But I do know that this reckoning that so many organizations have been going through is important, it's long overdue, and it must result in workplaces where all women, all people, feel safe and respected."
Later in the show, NBC's Megyn Kelly, who has written about being sexually harassed by former boss Roger Ailes at Fox News Channel, noted the anguish on the faces of her colleagues but said, "What we don't see is the pain on the faces of those who found the courage to come forward, and it is still a terrifying thing to do."
Kelly fills the time slot where Billy Bush worked until a year ago, before he lost his job after being caught on an "Access Hollywood" tape in sexually graphic banter with future President Donald Trump.
On Twitter on Wednesday, Trump said, "Wow, Matt Lauer was just fired from NBC for 'inappropriate sexual behavior in the workplace.' But when will the top executives at NBC & Comcast be fired for putting out so much Fake News."
Trump also alluded to potential misconduct by three other NBC News figures, while offering no details.
Natalie Morales, a former "Today" show colleague who left the show for "Access Hollywood" last year, said she was in shock about the story. She referred to stories that said she and Lauer had an affair, which they both denied.
"I have personally dealt with rumors in the past few years that were hurtful to me and to my family," she said. "They diminished my hard work. I've addressed these rumors head-on in the past. It's not the story today."
Another former "Today" host, Deborah Norville, said she was stunned by the news.
"As a journalist, it's upsetting to see another from our ranks caught up in these kinds of scandals. But as we've seen, no profession is immune," she said. "Sadly, I doubt if anyone will be surprised if there are similar headlines to come."