John Artis, a longtime friend and caregiver, said Carter died in his sleep today. Carter had been stricken with prostate cancer in Toronto, the New Jersey native's adopted home.
Carter spent 19 years in prison for three murders at a tavern in Paterson, New Jersey, 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.
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.