Elaine Bredehoft says the Aquaman star has “excellent grounds” for the appeal as there was “so much” evidence that was not included during the trial.
Mr Depp sued his former partner over a 2018 op-ed written in the Washington Post, which his lawyers said falsely accused him of being physically and sexually abusive toward her while they were together.
Jurors at Fairfax County District Court, in Virginia, returned a verdict in favour of Mr Depp on Wednesday after the six-week long trial.
Speaking on US news programme Today, Ms Bredehoft was asked whether the actress would be appealing the verdict.
“Absolutely, and she has some excellent grounds for it,” she said.
“We even tried to get the UK judgement in to dismiss his case because he already had his shot and that was one of the issues.
“But also a number of evidentiary issues, there was so much evidence that did not go in.”
Mr Depp had previously lost a similar trial in the UK which he brought against the publisher of The Sun newspaper after an article, also written in 2018, which referred to him as a “wife-beater”.
But following the verdict on Wednesday the actor was awarded compensatory damages of 10 million dollars (£8 million) and a further five million dollars (£4 million) in punitive damages.
In a separate verdict, Ms Heard was awarded two million dollars (£1.6 million) in damages after her counterclaim against Mr Depp over comments made by his lawyer Adam Waldman, who allegedly referred to her abuse claims as a “hoax”, was found to be defamatory.
Asked if Ms Heard was able to pay the amount she now owed, Ms Bredehoft replied “oh no, absolutely not”.
Following the verdict, the actress said she was “heartbroken” but “even more disappointed with what this verdict means for other women”.
Ms Heard said the verdict “sets back the clock” and added that Mr Depp’s attorneys had succeeded in getting jury members to “overlook” freedom of speech.
“I’m sad I lost this case. But I am sadder still that I seem to have lost a right I thought I had as an American – to speak freely and openly,” she said, in a statement shared on social media.