Hackett, who will link up with his new team-mates on Thursday, will stay at Adams Park until March 20.
The 28-year-old becomes the second signing of the day following Craig Eastmond's arrival from Arsenal.
Manager Gary Waddock told the club's official website: "He's got experience of playing at Championship level and knows League One after his loan spell at Exeter earlier this season.
"We're looking for a spark and hopefully these two additions will provide that."









