The Blues did not release salary terms, but multiple media sources have reported the deal is worth $4 million.
"Coming to a young, skillful team like this, with a ton of grit, was right in my wheelhouse," Roy told the St. Louis Post-Dispatch when the sides agreed to terms. "I want to win a Stanley Cup, and I thought this team was on the verge of becoming a great contending team."
Roy, 30, split last season between the Dallas Stars and Vancouver Canucks. He posted 22 points (four goals) and four penalty minutes in 30 games with the Stars. He then had six points (three goals) and two penalty minutes in 12 games with the Canucks, who acquired him in early April. Roy appeared in four Stanley Cup Playoff games with Vancouver, contributing one assist and two penalty minutes during a four-game loss to the San Jose Sharks.
"[Roy] is a playmaking centerman and he's just 30 years old," general manager Doug Armstrong told the Post-Dispatch. "I think it's a great opportunity for Derek to re-establish himself."
Roy spent his first eight seasons with the Buffalo Sabres, who took him in the second round (No. 32) of the 2001 NHL Draft. He has 168 goals, 455 points and 337 penalty minutes in 591 regular-season games, and seven goals, 26 points and 36 PIM in 45 playoff games.