Elliott appeared in 31 games for the Blues last season, posting an 18-6-2 record. He ranked second in the league with a 1.96 goals against average and 11th in both save percentage (.922) and shutouts (four).
The 29-year-old from Newmarket, Ont., has a 116-77-23 record, 2.48 goals against average, .910 save percentage and 25 shutouts in 235 career regular season games with Ottawa, Colorado and St. Louis.
Elliott's extension and the emergence of young goaltender Jake Allen leave the future of free-agent goaltender Ryan Miller in question. Miller was acquired by St. Louis from Buffalo at the trade deadline, but the star goaltender failed to help the Blues advance past the first round of the playoffs.