Maroon grew up in a St. Louis suburb and played for the St. Louis Bandits of the North American Hockey League.
"We're excited to add Pat Maroon to our group," Blues general manager Doug Armstrong said, according to the team's website. "Things picked up over the last few days, and last night about 10:30 p.m. I got a call from him and his representative saying they'd like to be part of the St. Louis Blues."
Maroon went into last season as a big part of an up-and-coming Edmonton team. He was coming off a 27-goal season and the Oilers' first playoff appearance in a decade. But Edmonton stumbled badly, and Maroon was dealt to New Jersey at the trade deadline to help the Devils' playoff push.
The 30-year-old had 13 points in 17 games for New Jersey in the regular season but had one goal as the Devils lost in five games to Tampa Bay in the first round of the playoffs.
Still, Maroon had a career-high 43 points last season.
He underwent surgery to a repair a herniated disk in his back in May.
"This is a one-year opportunity for him to come back, hopefully play with some really good centermen and get back to that 27-goal performance he had in Edmonton, or close to it," Armstrong said.