Bouwmeester, 29, has scored six goals and notched nine assists in 33 games this year for the Flames, who are out of playoff contention in the Western Conference.
The Blues, however, are in a dogfight for the eighth and final post-season slot in the West, and moved to obtain the blueliner in exchange for a conditional first-round draft pick, defenseman Mark Cundari and goaltender Reto Berra.
If Bouwmeester helps St. Louis make the playoffs, the first-round pick will come in this year's draft. If not, Calgary gets a 2013 fourth-round pick and a 2014 first-round selection.
Bouwmeester, a 2002 first-round pick for Florida, has compiled 71 goals, 229 assists and 463 penalty minutes over 750 career games with the Panthers and Flames.