Parayko, who was entering the final year of his previous deal, will now be under contract through the 2029-30 season.
"I can't wait to wear the Blue Note for another nine years," Parayko said in a statement. "St. Louis has been my home now for six seasons, and this is where I want to be. All the relationships I've gained, the teammates I've had, and the organization have all had a big impact on me. Winning here in 2019 was special, and I want the chance to stay here and do that again."
The 28-year-old has grown into a fixture on the Blues' blueline throughout his 418-regular-season game tenure with the club, tallying 41 goals and 130 assists to go along with a plus-54 rating.
In the playoffs, he's dressed in 70 games, scoring eight times and assisting on 19 others.