The St. Louis Post-Dispatch reported that the deal will pay Allen $2.2 million in the first year and $2.5 million in the second year.
Allen, 24, was selected in the second round of the 2008 draft. Over 37 games this season, the Fredericton, New Brunswick native recorded a 2.28 goals-against average and a .913 save percentage.
The Blues recorded a 51–24–7 record and earned the No. 1 seed in the Western Conference before being upset by the Minnesota Wild in the first round of the playoffs.
Allen, who had been a restricted free agent, has posted a 31–11–4 record overall. He tweeted in celebration of his new deal on Friday.