World number three Zverev was defeated by Medvedev in the group stage, but the German prevailed 6-4 6-4 in the final for his tour-best sixth trophy of the year.
The 24-year-old fired eight aces on his way to a deserved win over Medvedev, secured in just an hour and 15 minutes.
"It was great," Zverev said in his on-court interview. "I won the Finals, with a win in the final against someone I had lost [against] five times in a row, so I had to play one of my best matches.
"I am happy about that and happy to go on holiday with this win."
Building on his semi-final victory over Novak Djokovic, Zverev made a strong start in Turin and broke his opponent in the third game.
Medvedev was unable to hit back as Zverev dominated behind his first serve to see out the first set.
The Russian's hopes of becoming the first repeat champion since Djokovic's four in a row between 2012 and 2015 were further dented when losing serve in the opening game of the second set.
Putting his powerful game to good use, Zverev only improved as the contest went on at the Pala Alpitour venue as he saw the job through with his first match point to cap the year in style.