Furlong, who is highly-rated at Loftus Road, enjoyed a two-month loan spell at Northampton Town earlier this season, making 11 appearances for the Cobblers.
The full-back impressed during his time at Sixfields and now League Two Cambridge United have moved to take him to the Abbey Stadium on loan.
Cambridge boss Shaun Derry is keen to build a side capable of challenging for promotion this season and he sees Furlong as a key addition to his defence.
Furlong is set to go straight into the Cambridge squad for this weekend's clash with Crawley Town.
Furlong made his debut for QPR in the Premier League last season, making three appearances in the side after catching the eye in the club's under-21s.
The 20-year-old, who is the son of former QPR striker Paul Furlong, is highly-regarded within the corridors of power at Loftus Road, but the club are happy to loan him so that he can get valuable first-team action to continue his development.