Sundqvist, 25, has dressed in 44 games this season, tallying 20 points (11 goals, nine assists) and 20 penalty minutes.
The 6-foot-3, 209-pound forward was originally acquired by the Blues via trade from the Pittsburgh Penguins on June 23, 2017. Overall, the Boden, Sweden, native has amassed 60 points (27 goals, 33 assists) and 62 penalty minutes in 188 career regular-season games.