Johnny Depp has told a US court that over time his marriage to Amber Heard had begun to feel like he was "in a relationship" with his mother.

The actor said his former partner, who he is suing for defamation in Virginia, had a "need for conflict" and "couldn't be wrong".

"Things started coming up and I was suddenly just wrong about everything if I made a statement about something that I had been familiar with … I was suddenly wrong," he said, giving evidence on Wednesday in Virginia.

Amber Heard

"Then, beyond that, if you tried to explain yourself and correct the problem, the misunderstanding, it would then begin to heighten as Ms Heard was unable to be wrong.

"It just didn’t happen, she couldn’t be wrong."

He continued: "At a certain point what enters your mind (is) you start to realise you are in a relationship with your mother, so to speak.

"I know that sounds perverse and obtuse, but the fact is that some people search for weaknesses in people, that is to say sensitivities."

Mr Depp also said that he was "more inspired" to use drugs and alcohol due to Ms Heard's behaviour and their "constant clashes".

"It breaks you down, the constant haranguing breaks you down," he told the court.

"Yes, I was more inspired by Ms Heard to reach out for a numbing agent because of the constant clashes.

"There wasn’t a day that she would wake up and you’d expect something would hit the fan, and pretty much like clockwork it did.

"I had to have something to distance me and distance my heart from those verbal attacks, I had to have something to be able to maintain me."