Poulin has claimed a spot in the Nationals' Opening Day bullpen, Jessica Camerato and Paige Leckie of MLB.com report.
The 29-year-old will be one of three left-handers in the Washington bullpen, joining Cionel Perez and Ken Waldichuk. Poulin looked good this spring, posting a 0.00 ERA and 10:3 K:BB in 7.2 innings, but he may not see regular high-leverage work after producing a 3.65 ERA, 1.46 WHIP and 27:13 K:BB over his first 24.2 big-league innings last season with two wins, a save and five holds in 28 appearances.