He had been stricken with prostate cancer in Toronto, the New Jersey native's adopted home. John Artis, a longtime friend and caregiver, said Carter died in his sleep.
Carter spent 19 years in prison for three murders at a tavern in Paterson, N.J., in 1966. He was convicted alongside Artis in 1967 and again in a new trial in 1976.
Carter was freed in November 1985 when his convictions were set aside after years of appeals and public advocacy. His ordeal and the alleged racial motivations behind it were publicized in Bob Dylan's 1975 song "Hurricane," several books and a 1999 film starring Denzel Washington, who received an Academy Award nomination for playing the boxer turned prisoner.
Carter's murder convictions abruptly ended the boxing career of a former petty criminal who became an undersized middleweight contender largely on ferocity and punching power.
Although never a world champion, Carter went 27-12-1 with 19 knockouts, memorably stopping two-division champ Emile Griffith in the first round in 1963. He also fought for a middleweight title in December 1964, losing a unanimous decision to Joey Giardello.
In June 1966, three white people were shot by two black men at the Lafayette Bar and Grill in Paterson. Carter and Artis were convicted by an all-white jury largely on the testimony of two thieves who later recanted their stories.
Carter was granted a new trial and briefly freed in 1976, but sent back for nine more years after being convicted in a second trial.
"I wouldn't give up," Carter said in an interview on PBS in 2011. "No matter that they sentenced me to three life terms in prison. I wouldn't give up. Just because a jury of 12 misinformed people ... found me guilty did not make me guilty. And because I was not guilty, I refused to act like a guilty person."
Dylan became aware of Carter's plight after reading the boxer's autobiography. He met Carter and co-wrote "Hurricane," which he performed on his Rolling Thunder Revue tour in 1975.