Hulse is well down the pecking order at Loftus Road and has not featured for them this season after being left out of their 25-man Premier League squad.
The 33-year-old has only recently returned to QPR after a three-month loan spell at Charlton.
Hulse scored three goals in 15 appearances for the Addicks and impressed during his time at the Valley.
Millwall have moved to bring in Hulse as they are in the market for striking reinforcements after seeing Darius Henderson leave for Nottingham Forest.
Lions boss Kenny Jackett sees Hulse as a key addition to his squad for the remainder of the season as they look to maintain their push for promotion to the Premier League.