Halak, sent down to the minors on Dec. 31, was called up by the NHL club on Thursday.
In his last game with the Islanders, Halak gave up four goals in less than two periods of a 6-4 loss at Minnesota on Dec. 29. He was waived the next day.
Halak was 6-8-5 with a 3.23 goals-against average in 21 games this season before being sent down to Bridgeport of the AHL after clearing waivers. The 31-year-old was 17-7-3 with a 2.15 GAA in 27 games with the Sound Tigers.
Halak, an 11-year veteran who set the franchise record for wins two seasons ago, now rejoins an Islanders team that has climbed from the bottom of the Eastern Conference standings into the playoff race in his absence. New York heads into its final 10 games trailing Boston by two points for the East's second wild card.