Schenn's new deal comes off his fourth straight season in which he scored at least 50 points. He tallied 17 goals and 37 assists in 2018-19.
The contract ties Schenn to the Blues through the 2027-28 season.
Schenn joined the Blues in the 2017 offseason after the Philadelphia Flyers traded him. He won his first Stanley Cup with St. Louis last season.