The 58-year-old actor said he is “ashamed” of the 2013 text exchange which was never intended to be public, but blamed it on “irreverent and abstract humour”.
Depp started the conversation by telling his Mortdecai co-star: “Let’s burn Amber.”
Bettany replies to say: “Having thought about it I don’t think we should burn Amber – she’s delightful company and easy on the eye, plus I’m not sure she’s a witch. We could of course do the English course of action in these predicaments – we do a drowning test. Thoughts? NB I have a pool.”
Depp then says: “Let’s drown her before we burn her!!! I will f*** her burnt corpse afterwards to make sure she is dead.”
Giving evidence in his libel battle against Heard, Depp said they were “private texts” that needed to be put “in context”.
“It’s important to know none of that was ever intended to be real and the language used which … yes, I am ashamed (of) has to be spread on the world like peanut butter”, he told the court in Virginia.
“For example, the text that is about burning Ms Heard is directly from Monty Python and the sketch about burning witches and then drowning the witches.
“This is a film we’d all watch when we were 10 – it’s just irreverent and abstract humour.”
Depp went on to tell jurors Heard “despised” Bettany because of their friendship, claiming: “For her he was a threat and would take me away from her.”
Depp is suing the Aquaman star, 35, over a 2018 Washington Post op-ed piece on domestic abuse, and insists he was never violent during their marriage.
Heard, who is fighting the $50 million libel claim, has countersued for $100 million over Depp’s allegations that she has invented the abuse.
In his final day of evidence on Monday, Depp said reading the Washington Post article felt like being “hit over the head with a two-by-four”.
He claims the op-ed derailed his career, but Heard’s legal team introduced news articles from the years before 2018 to suggest Depp’s career was already on the rocks.
The actor dismissed them as “hit pieces” and “dreck”, a slang word for rubbish.
Extensive recordings of Depp and Heard arguing have been played to the court during the trial, with TV cameras trained on their faces as they listened.
Depp could be seen grimacing while Heard appeared close to tears as they listened to clips of the Pirates of the Caribbean actor insulting his then-wife about her weight.
At one stage, Heard shouts at Depp that he can put his “cigarettes out on someone else”.
The star told the court: “If anyone had a problem with my drinking, at any time in my life, it was me. The only person I’ve ever abused in my life is myself.”
Concluding his testimony, the court was played a clip of Heard saying: “Tell the world Johnny, tell them I Johnny Depp, a man, am a victim too of domestic violence?”.
Asked by his lawyer, Camille Vasquez, what he had said in response, Depp said: “I said yes, I am.”
After Depp’s evidence concluded, the court heard from his house manager in Australia, Ben King, who found the star’s severed finger after a 2015 incident.
Depp says his finger was injured when Heard threw a vodka bottle at him, but she says the wound was self-inflicted.
On Tuesday, the estate manager on Depp’s private Caribbean island, Tara Roberts, is expected to give evidence.
The trial continues.