Elmer Geronimo PrattHe was 63. Stuart Hanlon, a San Francisco-based lawyer who helped overturn Pratt's murder conviction, said he did not know the exact cause of death.
Pratt died in a small village in Tanzania where he lived with his wife and child, Hanlon said.
Hanlon called Pratt a "true American," saying that he was an Army veteran who served two tours in Vietnam before joining the Black Panther Party.
"He could've been a great leader. He was very charismatic," Hanlon said. "His legacy is that he never gave up. He never got despondent or angry."
Pratt's conviction became a rallying cry for rights groups that said he had been framed for his strident activism during the turbulent civil rights era.
Pratt was convicted for the 1968 murder of Caroline Olsen on a Santa Monica tennis court. He spent 27 years in prison before the conviction was overturned in 1997 after a judge ruled that prosecutors had concealed evidence.
The victim's husband, wounded during the robbery attempt, originally identified another man as the killer. But the jury was not informed of that, the judge said.
Famed attorney Johnnie Cochran also helped in the legal battle to get Pratt released from prison. Pratt spoke at Cochran's funeral in 2005.
After his release, Pratt told CNN that he held no bitterness about the many years he spent behind bars.
"I don't think bitterness has a place. I'm more understanding," Pratt said in a 1999 interview. "Understanding doesn't leave any room for bitterness or anger."
Of the 27 years he spent in prison, Pratt said eight was in solitary confinement. He said his spirituality and love of music helped him through that period.
"My mantra was the blues. It would go through my head when I was going through my meditations," Pratt said.