He actually did not. Out of the two of them, Amber was found to be liable for defamation for her accusations. Depp was found liable for his lawyer's words on specific facts about whether or not police were called a second time in a specific incident where Depp was not present, and no injuries were documented by the police.

Depp lost a defamation suit against the Sun for calling him a wife beater, because the judge found it to be enough due diligence for the Sun to have believed Amber.
In that trial, Amber was a witness not a party, and as such did not need to go through an adverse process or submit to rigorous cross-examination. Yet she still submitted, I think, seven iterations of her written testimony, because it kept having parts of it fully disproven by other witnesses or proven facts. Due to the different system in the UK, that was apparently fine.
I'm not well versed in the Sun/Depp case, because it was not a public casem and all I've seen are a few court documents. The Depp/Heard trial is available on YouTube and I recommend just watching Amber's testimony to anyone who is too busy to watch several weeks of trial. Her own words were plenty to disillusion me, at the very least.

I'm pretty sure they were both awful people accusing each other of awful shit that really deserved each other.