Collins had his contract purchased from Triple-A Syracuse on Tuesday, Jamal Collier of MLB.com reports.
The 28-year-old southpaw compiled a 2.77 ERA and 1.54 WHIP across 13 innings (17 appearances) with the Nationals before getting designated for assignment earlier in the year. Collins is expected to take the roster spot of Ryan Madson (back), who was not listed on the lineup card Tuesday.