Belfour, a two-time Vezina Trophy winner who ranks third all-time among NHL goalies with 484 wins, played 18 seasons with Chicago, San Jose, Dallas, Toronto and Florida.
"Ed is one of the winningest goaltenders in National Hockey League history and we're thrilled to have him on our staff," Blues president John Davidson said in a statement Thursday.
"His knowledge of the position will be invaluable for our goaltenders in Peoria and our young goalies in our organization."
Belfour, 44, posted a 484-320-125 record with a 2.50 goals against average and 76 shutouts over 963 career games. The five-time all-star appeared in three Stanley Cup finals, winning one in 1999 with the Stars.