The 27-year-old - who has not been beaten in two years - edged out Ehsan Hadadi, who won Iran's first ever Olympic medal in athletics with a throw of 68.18m and had led until the penultimate round.
Defending champion Gerd Kanter of Estonia was third with a season's best of 68.03m.
Harting celebrated his victory by clearing several of the the barriers set up for the women's 100m hurdles - and did so with style for such a big man.
Hadadi had taken the lead in the first round with a throw of 68.18m while both Harting and Lithuania's two-time Olympic champion Virgilius Alekna also put down markers in the opening salvo.
Kanter improved in every round and moved into second with his superb season's best effort in the penultimate round which pushed 40-year-old Alekna out of the medal positions.
Harting too found his best form in the same round to throw his winning effort and Hadadi then replied with an enormous effort only to have it ruled out for a foot fault.
The German failed to improve on it in the final round but Hadadi was unable to find the inspiration to deny him his moment of glory and become the first from his country to win the event since Lars Riedel in Atlanta in 1996.
Tuesday was an altogether more successful day for the German Olympians, with silver medals in the team dressage, two more in the men's gymnastics, and a guaranteed silver in the men's beach volleyball, where Julius Brink and Jonas Reckermann reached the final.
Defending weightlifting champion Matthias Steiner suffered a shock when the 196-kilo bar he was attempting to lift slipped from his grasp and fell onto his neck.
He managed to walk away and was taken to hospital for checks, but seems to have escaped serious injury.