An NBC internal investigation of former “Today” host Matt Lauer has concluded there was “no evidence” that senior executives at the network were aware of Lauer’s long history of alleged workplace sexual harassment until a complaint emerged about him in November.

The findings, based on interviews with 70 current and former employees over five months, were released Wednesday. The seven-page report drew immediate criticism from outside groups and advocates who said the network’s investigation lacked independence.

Lauer, the star of NBC News’s most lucrative program, was fired in November after an unidentified colleague filed a formal complaint alleging inappropriate sexual behavior. Three other women subsequently made allegations against him.

Some of the women told Variety they complained about him to senior managers, but that the allegations were ignored. The Washington Post reported last month that Lauer’s former “Today” co-host Ann Curry said she approached two members of NBC’s management team in 2012 after a female staffer told her she was “sexually harassed physically” by Lauer.

The network confirmed in its investigation that four women complained about Lauer. But it explicitly contradicted Lauer’s accusers, saying senior managers became aware of concerns about him only last fall. The investigation was overseen by Kim Harris, the general counsel at ­NBCUniversal, the parent company of NBC News. NBC said it also consulted with two outside law firms.

The report said the first formal complaint about Lauer was made by an unidentified employee on Nov. 22. She alleged in an internal interview a week later that Lauer had engaged in “inappropriate sexual behavior in the workplace.”

Lauer admitted to the alleged behavior during an interview with NBC’s legal and human-resources staff on Nov. 28, the report said. He was fired that day.

Three more employees subsequently came forward with complaints, according to the investigation, which dated these allegations to 2000, 2001 and 2007.

In addition to interviews, the investigative team searched emails by Lauer, NBC News executives and “Today” supervisors, according to the report. The team also scoured texts on Lauer’s company phone, complaints to NBC helplines, and legal and HR records.

“We found no evidence indicating that any NBC News or Today Show leadership, HR or others in positions of authority in the News Division received any complaints about Lauer’s workplace behavior prior to Nov. 27, 2017,” the investigation concluded. “All four women who came forward confirmed that they did not tell their direct manager or anyone else in a position of authority about their sexual encounters with Lauer. Current and former members of NBC News and Today Show leadership, as well as News HR, stated that they had never received a complaint about inappropriate workplace behavior by Lauer, and we did not find any contrary evidence.”

The finding effectively clears NBC News Chairman Andrew Lack, a longtime friend of Lauer, and the division’s president, Noah Oppenheim, of suspicions that they covered up complaints. Lauer was one of their most valuable employees, a mainstay of the network’s morning franchise.

However, the investigation did not address allegations of harassment against former NBC anchor Tom Brokaw. Linda Vester, a former NBC News correspondent, said last month that Brokaw had harassed her in the 1990s when they worked at the network.

Lauer’s workplace misconduct apparently began more than 20 years ago; in 1996, according to the investigation, one of the women who eventually complained about him said he put his hand on her thigh and made “a sexually suggestive” comment. She reported this interaction to her manager, who decided that the woman would no longer be assigned to projects that required her to travel with Lauer. The manager didn’t report this interaction to any senior executives, investigators said.

The report clarifies Curry’s claim that she alerted management to complaints about Lauer’s behavior in 2012. It says that Curry, during an interview with investigators, “confirmed that she did not disclose to anyone in management that she had received a specific complaint.”

Curry declined Wednesday to comment on the report. But in an interview in April, she said she didn’t provide details of a colleague’s harassment complaint to management because she promised the woman anonymity. She told The Post that she warned two members of NBC management that they needed to keep an eye on Lauer and his behavior toward women, but she offered no names or other specific information.

The report suggests employees were aware of Lauer’s marital problems and knew he had had extramarital affairs but assumed, “with limited exceptions,” that the affairs were with women outside NBC, according to the report.

“A number of individuals interviewed said that Lauer could be flirtatious, would frequently make jokes, some with sexual overtones, and would openly engage in sexually-oriented banter in the workplace,” the report says.

Several women described to investigators what they believed was a sexual overture from Lauer when he complimented them on their appearance in “sexually suggestive ways.” But the women said they deflected Lauer’s comments, and he did not pursue them.

Critics of the investigation faulted its in-house perspective. “There is an inherent conflict of interest when management reviews itself,” said Eleanor McManus, co-founder of Press Forward, an organization formed by current and former TV journalists to address harassment.

Ari Wilkenfeld, an attorney for one of Lauer’s accusers, said NBC’s conclusions “demonstrate why an outside investigator is preferable” to an internal report. “The report itself acknowledges that people were and are still uncomfortable coming forward,” he said. “And there is no way NBC will be able to uncover the full extent of the problem so long as the interviewers and the interviewees receive paychecks from the same company.”

The report also addressed a notorious element of the Lauer scandal: the existence of a button in his office that allegedly locked the door remotely. It said the button was “a commonly available feature” in NBC’s Rockefeller Center offices in New York and that, contrary to some reports, it doesn’t lock the door from the inside.

It concluded by generally absolving NBC regarding its larger workplace culture: “The investigation team does not believe that there is a current widespread or systemic pattern of behavior that violates company policy or a current culture of harassment in the news division, based on our interviews . . . and our review of the nature and number of workplace complaints in the news division.”

But it added that “more work needs to be done to ensure that all employees . . . feel comfortable ­reporting concerns and do not fear retaliation if they do.” It recommended training, better communication from management and improvements to employee complaint-reporting channels.

In a memo to employees on Wednesday, Lack wrote: “We cannot change the past. What we can do is learn from it, and try to make it right.” He offered a seven-point plan for “a safer and more respectful environment,” including more training for managers, mandatory workplace training and “constant vigilance, monitoring and measuring progress.”

Sarah Ellison contributed to this report.