ABC canceled the hit sitcom “Roseanne” on Tuesday hours after the show’s star and co-creator, Roseanne Barr, posted a racist tweet about a former top adviser to President Obama who is black.

Early on Tuesday, Ms. Barr posted a comment about Valerie Jarrett, the former adviser to Mr. Obama, that said if “muslim brotherhood & planet of the apes had a baby=vj.”

Ms. Barr, whose ABC sitcom about the Conner family ended a successful comeback season last week, initially dismissed accusations that the comment was racist, defending it as “a joke.” She also said on Twitter, “ISLAM is not a RACE, lefties. Islam includes EVERY RACE of people.”

Ms. Barr later deleted the post about Ms. Jarrett, and initially said nothing about the reference to “The Planet of the Apes.” About a half-hour later, she offered an apology.

https://twitter.com/therealroseanne/status/1001471669641216005

Ms. Barr also said she was “leaving Twitter.”

Hours later, ABC canceled her show.

“Roseanne’s Twitter statement is abhorrent, repugnant and inconsistent with our values, and we have decided to cancel her show,” ABC’s entertainment president, Channing Dungey, said in a statement.

The fallout over the Twitter post had begun earlier. Wanda Sykes, the black comedian who served as a consulting producer on “Roseanne” this season, said she was leaving the sitcom. Whitney Cummings — a showrunner for the revived comedy, and one of its most outspoken liberal supporters — had already left the series this month.

I will not be returning to @RoseanneOnABC.

— Wanda Sykes (@iamwandasykes) May 29, 2018

The Rev. Al Sharpton said that Ms. Barr’s comparing Ms. Jarret to an“APE is racist and inexcusable. ABC must take action NOW!” Tom Arnold, Ms. Barr’s former husband and co-star, called her Twitter posts “dangerous.” And the MSNBC host Joe Scarborough said, “There is no apology she can make that justifies @ABC turning a blind eye to this bigotry by airing another second of her show.”

On Tuesday, before she apologized, Ms. Barr had an exchange with Chelsea Clinton after Ms. Barr referred to Ms. Clinton as “Chelsea Soros Clinton,” a reference to George Soros, the billionaire liberal donor who is often the focus of conservative critics. Donald Trump Jr. shared one of Ms. Barr’s posts in the exchange.

Sorry to have tweeted incorrect info about you!I Please forgive me! By the way, George Soros is a nazi who turned in his fellow Jews 2 be murdered in German concentration camps & stole their wealth-were you aware of that? But, we all make mistakes, right Chelsea?

— Roseanne Barr (@therealroseanne) May 29, 2018

Ms. Barr’s often incendiary use of Twitter has stayed in the background amid the “Roseanne” revival’s success.

Months before the show premiered, she said that her children had taken her social media accounts away from her. It was no small matter: Ms. Barr has used Twitter to promote conspiracy theories, and some ABC executives were worried that she might say something offensive enough to lead viewers or advertisers to revolt.

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Ms. Barr has been outspoken in her support of President Trump, who called to congratulate her on the ratings for the show’s premiere episode, and in her antipathy toward Hillary Clinton.

[Read an interview with Ms. Barr, in which she touches on her and her character’s support of President Trump.]

But as viewers flocked to “Roseanne,” to the delight of ABC executives, Ms. Barr returned to Twitter. None of her posts threatened the show’s success, although some did attract scrutiny. One of Ms. Barr’s messages accused a survivor of the high school shooting in Parkland, Fla., of giving a Nazi salute; another involved a conspiracy theory about Mr. Trump quietly breaking up a child sex trafficking ring including prominent Democrats.

Sorry to have tweeted incorrect info about you!I Please forgive me! By the way, George Soros is a nazi who turned in his fellow Jews 2 be murdered in German concentration camps & stole their wealth-were you aware of that? But, we all make mistakes, right Chelsea?

— Roseanne Barr (@therealroseanne) May 29, 2018

ABC was able to sidestep controversy in both instances.

“You can’t control Roseanne Barr,” Ben Sherwood, the president of Walt Disney Company’s and ABC’s television group, said in an interview with The New York Times in March, when asked about her Twitter account. “Many who have tried have failed. She’s the one and only.”

There have been other sources of controversy.

The revival’s third episode featured a joke about two ABC comedies with diverse casts, “black-ish” and “Fresh Off the Boat.” Ms. Barr’s character and her husband, Dan, played by John Goodman, wake up on the their living room couch, having fallen asleep in front of the television. “We missed all the shows about black and Asian families,” Dan Conner said. To laughter from the show’s studio audience, Roseanne Conner responded, “They’re just like us. There, now you’re all caught up.”

[The “Roseanne” revival suggested that “as long as you’re good to your neighbors individually, it doesn’t matter how you treat people in the aggregate,” wrote our critic.]

The joke prompted an outcry but ABC defended the show. “We felt writers were looking to tip a hat to those shows,” Ms. Dungey said this month. “It certainly wasn’t meant to offend. I do stand by the ‘Roseanne’ writers.”

Even as the “Roseanne” revival experienced success, ABC’s relationship with the “black-ish” showrunner, Kenya Barris, deteriorated. The network made the rare decision earlier this year to pull an episode of the show, which is known for its frank assessment of race relations. The episode involved the main character, Dre, raising socially fraught issues while telling a bedtime story to his son. Mr. Barris is in negotiations to leave his ABC contract and begin working with Netflix.

“Roseanne” will probably finish the 2017-18 television season as the No. 3 rated show, behind two NBC programs: “Sunday Night Football” and “This is Us.” More than 18 million people on average have watched “Roseanne” this season, according to Nielsen’s delayed viewing data.

The show was a boon for ABC, and part of a strategy to appeal to viewers in the American heartland. “Roseanne” had nine episodes this past season, and it was scheduled to return in the fall with another 13. When ABC hosted a showcase for advertisers two weeks ago to preview its fall lineup, “Roseanne” took center stage.

“If anyone came to play a drinking game for the number of times we mention Roseanne,” Mr. Sherwood said from the stage at Lincoln Center’s David Geffen Hall, “you’re welcome.”

[Read more about ABC’s strategy to reach out to America’s heartland after the election of President Trump.]

Ms. Barr may have been front and center then, but the series was an afterthought on the Walt Disney Company’s most recent earnings call with investors. Despite its outsize success, “Roseanne” was not mentioned in the company’s prepared remarks, and it was only referenced after an investor asked a question about how the company felt about the network’s position going into a new TV season.