In a sport where competitors rarely competed at more than one Games, Trentin was only the second man to win multiple medals in the track time trial.
Italy's four-Games medal streak in the event ended as Gianni Sartori took fourth.
The two-time reigning world champion, and favorite in this race, was Niels Fredborg of Denmark.
Gianni Sartori, the amateur world record holder, and Trentin were also significant contenders.
That Olympic mark held until rider #24, Pierre Trentin, who broke the world record at 1:03.91.