The Dutchman will spend the remainder of the season with the Swans, subject to international clearance.
26-year-old Fer, who scored an absolute bottler against the Welsh club last season, follows Italian striker Alberto Paloschi to the Liberty Stadium after he joined from Chievo last week.
Fer has been at Loftus Road since the summer of 2014 having joined from Norwich City after one season at Carrow Road.
.@LeroyFer10 will stay at the Liberty until the end of the season, subject to international clearance. #swanspic.twitter.com/qZ7K8cFoN6
— Swansea City AFC (@SwansOfficial) February 1, 2016