Felicia Sonmez, a reporter for The Washington Post who in recent days has been at the center of a debate over the organization’s social media policies and the culture of the newsroom, was fired on Thursday, according to three people with knowledge of the matter who spoke on the condition of anonymity to discuss personnel matters.

Ms. Sonmez was fired over email on Thursday afternoon, according to one of the people. In an emailed termination letter, which was viewed by The New York Times, Ms. Sonmez was told that The Post was ending her employment, effective immediately, “for misconduct that includes insubordination, maligning your co-workers online and violating The Post’s standards on workplace collegiality and inclusivity.”

The email, from Wayne Connell, the Post’s chief human resources officer, also said Ms. Sonmez’s “public attempts to question the motives of your co-journalists” undermined The Post’s reputation.

“We cannot allow you to continue to work as a journalist representing The Washington Post,” the letter said.

Ms. Sonmez’s internal Slack account was deactivated by Thursday afternoon, according to a screenshot viewed by The Times. Reached by phone, Ms. Sonmez said that a statement would be coming from The Washington Post Newspaper Guild.

The guild’s statement said it would not comment on individual personnel matters. “We represent and provide support to all members facing discipline,” it said. The news that Ms. Sonmez was no longer employed by The Post was reported earlier by The Daily Beast.

Ms. Sonmez, a national political reporter, sued the paper and several top editors last year, saying they had discriminated against her by barring her from covering stories about sexual assault after she had publicly identified herself as a victim of assault. The case was dismissed in March, with the judge noting that The Post had attributed the coverage bans not to her being a victim of sexual assault but to concerns that her public statements had created an appearance of bias. Ms. Sonmez’s lawyer at the time said she planned to appeal.

In the past week, she has been at the center of a public firestorm over the newsroom’s culture. On Friday, Dave Weigel, a political reporter at the paper, retweeted a sexist joke that implied women were either bisexual or bipolar. Ms. Sonmez then tweeted, “Fantastic to work at a news outlet where retweets like this are allowed!”

Mr. Weigel apologized for the tweet. On Monday, he was suspended by The Post for a month without pay, according to a person with knowledge of the matter.

Ms. Sonmez then got into a Twitter disagreement with Jose A. Del Real, a reporter who acknowledged Mr. Weigel’s tweet was “unacceptable” but admonished Ms. Sonmez for “rallying the internet to attack” Mr. Weigel. Mr. Del Real later sent several tweets regarding an “unrelenting series of attacks” against him, and Ms. Sonmez questioned why The Post had not done anything to reprimand him for his tweets about her, including one that said she had engaged in “repeated and targeted public harassment of a colleague.”

In the following days, Ms. Sonmez wrote numerous posts on Twitter about the newsroom culture at The Post and what she said was the uneven way its social media policy was applied to different reporters. At times she jousted with fellow journalists at The Post on Twitter.

Many in the newsroom supported Ms. Sonmez throughout her lawsuit and were grateful to her for her advocacy for sexual abuse victims, according to two current Post employees, but the sentiment began to shift this week as she continued to tweet about The Post.

Some felt Ms. Sonmez was hurting the institution and disagreed with her use of public forums to criticize co-workers, the people said.

Others took issue with her response to an email from the national editor, Matea Gold, who had urged people to look after their mental health in the wake of the shootings last month in Buffalo, N.Y., and Uvalde, Texas.

Ms. Sonmez sent a reply-all to the newsroom saying that she had once been punished after telling an editor she needed to take a walk after reading a difficult story.

Ms. Sonmez defended herself in another set of tweets on Thursday morning, before she was fired, saying, “I care deeply about my colleagues, and I want this institution to provide support for all employees. Right now, the Post is a place where many of us fear our trauma will be used against us, based on the company’s past actions.”

The fracas has amounted to something of a leadership test for Sally Buzbee, who became the executive editor of The Post last June. Ms. Buzbee wrote two memos to the newsroom in the past week asking for colleagues not to attack each other on social media.

“The newsroom social media policy points specifically to the need for collegiality,” Ms. Buzbee wrote in an email on Tuesday.

Benjamin Mullin contributed reporting.