Depp and his producing partner Christi Dembrowski have optioned the film rights to Echols' unpublished memoirs, according to Deadline.com.
Their film will chronicle Echols' life and his time behind bars for a crime he insists he didn't commit. He was 18 at the time of his arrest.
Following the West Memphis Three's release from prison, Depp urged U.S. authorities to continue searching for the real killers of the Arkansas boy scouts - so Echols, Jason Baldwin and Jessie Misskelley, Jr.'s names could be cleared.
The three men were set free in August (11) after reluctantly admitting guilt. They later revealed they had only done this as part of an agreement that would lead to their release.
During an interview with Larry King on CNN Presents, Depp said, "Admitting guilt (while) maintaining innocence, it's a really floppy piece of ground to stand on. I knew immediately when I first started to familiarise myself with the case, I knew instantly that they were innocent, that they were wrongfully accused. The more research I did, the more people I spoke to, it was absolutely apparent...
"It was ugly and a raw deal from the get-go back in '93... When you're thinking of these three kids, one, Damien Echols, on Death Row for 18 years, spent 10 years in isolation, for a crime that he did not commit.
"What I'm hoping is that the investigation will continue outside of the courthouse right now and that we will be able to prove the real killers."
Depp isn't the only celebrity fighting for justice for the West Memphis Three - rocker Eddie Vedder and Dixie Chicks star Natalie Maines have been close to the case for years and moviemaker Peter Jackson has been quietly funding a private investigation into the murders.