Tretter, who is entering his eighth season, will take over for the departing Eric Winston, who had been in the position since March 2014.
Tretter was one of three candidates up for the position along with Buccaneers linebacker Sam Acho and Giants defensive back Michael Thomas. Tretter had been the Browns' third co-alternate representative with the NFLPA.
Tretter has started all 48 games since signing with the Browns in 2017. He graduated from Cornell University, where he earned a degree in industrial labor relations.
Check out behind the scenes photos of Browns coaches and executives watching combine workouts