The American news outlet had tried to stop Morgan Tremaine from taking the stand during the final week of the trial in Fairfax, Virginia.
So, who is Morgan Tremaine, what did he say on the stand, and why did TMZ not want him to give a testimony and what did the judge decide?
Here’s what you need to know.
Why has Morgan Tremaine been asked to testify in the trial?
During the ex-couple’s trial last month, the jury saw footage of Depp getting angry in their West Hollywood home as Heard recorded him.
Heard can be heard saying: “We’re not even fighting this morning. All I did was say sorry.”
Depp responded: “Did something happen to you this morning? I don’t think so! You wanna see crazy? I’ll give you f***ing crazy.”
The footage also showed him slamming kitchen cabinets and throwing a wine bottle.
During cross-examination on a previous day of the trial when the video was first mentioned, Depp’s attorney Camille Vasquez asked Heard about the leak and said it was likely the actor’s team will try to find out exactly where the video came from.
It is understood Tremaine was called to the stand to tell the court about what exactly the video showed and where it came from.
Why did TMZ try to stop him from testifying?
TMZ filed an emergency motion, asking the judge to prevent Tremaine from giving his testimony based on “journalist’s privilege”, according to court papers.
Lawyers for the California-based news outlet wrote in the papers that the company didn’t want him taking the stand and “disclosing TMZ’s privileged information” during his testimony.
In the motion, Charles Tobin, an attorney representing TMZ’s parent company, EHM Productions, said that the company’s concern relates to an article it published on 12 August 2016, called Johnny Depp Goes Off On Amber. . . Smashes Wine Glass, Bottle.
The court papers state that TMZ was given the video by a confidential source and that the company had promised that source they would not disclose their name.
The motion suggests the news outlet was concerned Tremaine would reveal the identity of the source.
What did the judge decide?
Before making a decision, Judge Penney Azcarate heard arguments on the motion in court on Wednesday 24 May.
The request was then denied because TMZ is not a party to the case and its arguments have no bearing on the defamation claims.
What did Morgan Tremaine say on the stand?
On Wednesday 25 May, Tremaine was called as a witness for Depp.
He said that the ending of the video which was played in court was different to the one that came in via TMZ’s email tip line in 2016.
Tremaine said the footage which was seen by the jury left out some key context, and said Heard could be heard “seemingly snickering” toward the end of the video.
He said: “When I had clicked the direct link that we received and watched the video in its entirety it was much shorter than the video we had received, the video that’s been played in this trial.
“There was a bit at the beginning that was played here in which Ms. Heard is seemingly sort of setting up the camera and getting into position.
“And then, there’s a bit at the end, where she is seemingly snickering and looks at the camera. That part was not present in what we received.”
He then testified that he did not know the source of the video transferred through the organisation’s email tip line.
He told the court: “The video was sent in through our email tip line, which is an email distribution that goes to all the producers and to myself as the field assignment manager, because it often included celebrity locations.
“I received that email and it included a link from some unknown, dropbox-type website.
“In that link was the video of Johnny Depp smashing the cabinets.”
The video was downloaded, given a watermark, and posted on the TMZ website within about 15 minutes.
Tremaine added: “The only way to obtain copyright over media would be if we shot it ourselves, [or] if it was sent to the tip line source-verified that it was from the original copyright owner and then either purchased from that person or given to us; the third option would be if it was directly given to us by the copyright holder, like a direct source.”
During his testimony, Tremaine also confirmed that he was asked by TMZ to send photographers to a Los Angeles courthouse on 27 May 2016 - the day Heard filed for a restraining order against Depp.
He said: "We were trying to capture Amber leaving the courthouse and an alleged bruise on the right side of her face.
"She was going to sort of stop and turn towards the camera to display the bruise on the right side of her face, the alleged bruise."
When asked if TMZ got the shot, he replied: "We did."
What was said during cross-examination?
Heard has denied working with TMZ.
During cross-examination of Tremaine, Heard’s lawyer Elaine Bredehoft accused him of seeking his "15-minutes of fame."
In response, he accused Heard’s legal team of the same thing by representing the actress.
He said: "I’m actually putting myself kind of in the target of TMZ, a very litigious organisation.
“And I’m not seeking any 15-minutes here. I could say the same thing about taking Amber Heard as a client, for you."
Who is Morgan Tremaine?
Morgan Tremaine, whose full name is Morgan Cliff Tremaine, is a former TMZ journalist, producer and assistant manager.
His verified Twitter account, which has over 14,000 followers, states he now works as a producer at Esports Engine, a turnkey esports solutions company that works with game publishers.
His biography states that he also works as a host, Xbox Ambassador, as well as a producer for Twitch Rivals, 100 Thieves and Pokemon and more.
He posted a tweet on the day he gave his testimony which read: “My statement: I genuinely hope no one is paying attention to this trial today, and are instead focused on stopping gun violence like that which killed 19 children and 2 teachers in Texas this week. Celebrity news does not matter.”
Tremaine was referring to the Texas school shooting which happened on Wednesday 25 May.
What is the defamation case about?
Depp launched the defamation case against Heard in 2019, after she wrote an opinion piece published in the Washington Post in December of 2018 in which she described herself as a victim of domestic abuse and thereby implicating him as an abuser.
Depp’s lawyers claim that the article falsely implies that Heard was physically and sexually abused whilst she was married to him.
The article doesn’t mention Depp by name, but he claims it has cost him acting roles and is suing Heard for $50m (£40m).
She has counter-sued him for $100m (£80m), claiming Depp defamed her when his legal team referred to her claims as “fake” and a “sexual violence hoax”.
The former couple have both accused each other of being physically violent during their relationship, and they each deny the other’s claims.
Depp and Heard met while they were filming the 2011 film The Rum Diary, in which they played lovers, and the two married in LA in February 2015.
In May 2016 Heard obtained a restraining order against Depp after accusing him of abuse, which he denied. Their divorce was finalised in 2017.