The 47-year-old musician is Depp's longtime pal, and godfather to the actor's 17-year-old daughter, Lily-Rose. "We go back," Manson said.
"Johnny is one of the nicest people that I know -- to the extent where it's almost heartbreaking how kind he is to his friends and everyone around him," Manson explained. "I know that he was completely crucified -- unjustly."
Manson, who will be guest starring on the third season of the WGN America show, Salem, when it returns in November, said he stood by Depp, who was the subject of domestic violence allegations during his split from Heard.
"As my friend, I know that he's handling it the best he can and he's a great dad, too," Manson continued. "It fills me with joy to see his kids grow up and be so smart, and so hilarious. We played a show together not too long ago. It's hard to say when you talk about your friends. Of course I think that all of it was bulls**t, and I think that he is a great person. I wouldn't agree with any of it if someone were to put me on the stand and ask me what I know, or what I've witnessed."
As part of their divorce settlement, Heard, 30, withdrew her request for a restraining order against Depp and issued a joint statement.
"Our relationship was intensely passionate and at times volatile, but always bound by love," the statement read. "Neither party has made false accusations for financial gains. There was never an intent of physical or emotional harm."
For more on the settlement, watch this video.