Heard made the allegation on the second day that she took the stand, telling the High Court: "[Johnny] was about to push [my sister] down the stairs and, the moment before that happened, I remembered information I had heard [that] he pushed a former girlfriend – I believe it was Kate Moss – down the stairs."
David Sherborne, Depp's lawyer, said the claim was "another moment of scripted malevolence" by Heard when she gave evidence, and called on Justice Nicol to conclude that she is an unreliable witness.
"We say that Ms Heard doesn't know what the truth means," Sherborne told the court. "Our position is quite simple. We say, from the big points to the small ones, Ms Heard has proven herself to be an unreliable witness and, quite frankly, a compulsive liar."
Sherborne said the Hollywood actress had "changed dates", "added further details" and "invented whole events" during her "performance" in the witness box.
The barrister said the court had heard "astonishingly self-serving and fictionalised accounts" of what Heard was thinking at the time of the alleged violence, and also referred to her "secret feelings book that reads more like a novella than anything which matches reality".
Sherborne refuted the "exceptionally serious" allegation of domestic abuse levelled at his client, saying that Depp is "no wife beater" and that his traditional "Southern gentleman" attitude meant he has never hit a woman in his life.
Rather, it was Heard who was the "abuser" in the relationship, he argued, as she had a "propensity to violence".
The court heard how Heard's father, David Heard, had previously sent a text to Depp saying his daughter "needs help with her temper".
Depp's legal team also criticised Heard's dishonest account of when she had taken illegal drugs.
"I have never come across, in any case, such deeply unreliable medical notes," Sherborne said. "They were right when it suited her and they were always wrong when it didn't. Sometimes notes, even in the course of her giving evidence, could be both right and wrong at the same time. How convenient.
"Doctors were lying, nurses were lying, police officers are lying. Only Ms Heard – who was at pains to repeat the well-rehearsed mantra that she was not here to call anyone a liar – only Ms Heard was correct at all times, no matter what."