It comes after Ofcom launched an investigation into remarks he made about the Duchess of Sussex on Monday's show that sparked more than 41,000 complaints.
After a clip aired of Markle discussing her issues with mental health and suicidal thoughts and royal officials’ knowledge of them, Morgan said: “I’m sorry, I don’t believe a word she says.
“I wouldn’t believe her if she read me a weather report.”
Tempers then flared on Tuesday’s show after Morgan walked off set when colleague Alex Beresford told him that Markle was “entitled to cut you off if she wants to”.
Morgan has since said he stands by his comments and told Sky News Meghan was "contemptible".
Morgan also released a statement on Twitter saying: "On Monday, I said I didn’t believe Meghan Markle in her Oprah interview. I’ve had time to reflect on this opinion, and I still don’t. If you did, OK. Freedom of speech is a hill I’m happy to die on. Thanks for all the love, and hate. I’m off to spend more time with my opinions."
But mental health charity Mind criticised Morgan’s comments on Monday, saying in a tweet that it was “disappointed and concerned”, adding: “It’s vital that, when people reach out for support or share their experiences of ill mental health, they are treated with dignity, respect and empathy.”
Addressing Morgan’s departure, Susanna Reid told GMB viewers on Wednesday that the show will be “very different” but “shows go on”.
She added: “He is without doubt an outspoken, challenging, opinionated, disruptive broadcaster…
“But now Piers has decided to leave the programme. Some of you may cheer and others may boo.
“He has been my presenting partner, Monday to Wednesday, for more than five years and during Brexit and the pandemic and other issues, he has been a voice for many of you and a voice that many of you have railed against.
“It is certainly going to be very different but shows go on and so on we go.”
Watch: Susanna Reid addresses Piers Morgan’s exit on GMB