Patrick Tenore told the Los Angeles Times Norton died of congestive heart failure while undergoing rehabilitation from a stroke suffered last year.
Norton, coming in as a 5-1 underdog, shot to fame with a March 31, 1973, title decision over Muhammed Ali in San Diego during which he broke the champion's jaw.
But he fell to Ali in a rematch later that year at Inglewood, Calif., as well as in a 1976 decision at Yankee Stadium in New York.
Norton finished his boxing career with a record of 42-7-1 and 33 knockouts.
Son Ken Norton Jr. was an NFL linebacker for the Dallas Cowboys and San Francisco 49ers and is now on the coaching staff of the Seattle Seahawks.