He stormed off the set during an argument with co-host Alex Beresford during a conversation about Meghan Markle and Prince Harry's blockbuster interview with Oprah Winfrey, which aired Monday in Britain.
Beresford accused Morgan of criticizing Markle so much because she ended her friendship with him after she met the prince. Morgan later returned to his seat — temporarily — but ITV announced later in the day that he had decided to leave for good.
His departure comes after Ofcom, the U.K. media regulator, launched an investigation into comments he made about Markle on Monday's edition of the morning show. More than 41,000 people complained about what he said then, primarily that he didn't believe her allegations about having been ignored when she sought help for her mental health.
"I'm sorry, I don't believe a word she said, Meghan Markle," Morgan had said. "I wouldn't believe it if she read me a weather report."
On Tuesday, he acknowledged that it's not for him to question what Markle had said about her own mental health.
It was a whirlwind of events and onlookers, including celebrities, had a lot to say.
Sharon Osbourne, who sat alongside Morgan when they both judged America's Got Talent, supported her friend while co-hosting The Talk.
She called him a royalist. "You fight for your queen and your country," she said.
Osbourne believes that Morgan was hurt "terribly" by whatever happened between him and Markle.
On social media, she wrote, "I am with you. I stand by you."
Actress Jameela Jamil, who's been vocal about her own mental health struggles, said Morgan's criticisms drove her to contemplate taking her own life just last year.
Meanwhile, Sunny Hostin, a co-host on The View, disapproved of Morgan's actions on her own show. "Watching him walk off like that, isn't it interesting that Piers Morgan can walk away from a slightly uncomfortable situation," she said, "but Prince Harry and Duchess Meghan cannot walk away from more than a slightly uncomfortable situation, but a situation that put her mental health and her life at risk." (Her comments begin at 3:08.)
Meanwhile, one of America's best-known morning TV personalities, Today weatherman Al Roker, was also not sad to see Morgan go.
Chelsea Handler echoed that point.
Actor George Takei joked that Morgan had "canceled himself."