Harriman, 20, is equally adept at right-back or central midfield and signed a two-year deal with the Premier League side last May after making two substitute appearances for the West London outfit during the 2011/12 campaign.
“He was coming through the ranks when I was at QPR and was making big noises in the youth team,” Gareth Ainsworth told wwfc.com.
“He’s progressed since then and is a quality player. We’re looking forward to having him in the group.”
Harriman, who will wear number 23, goes straight into the squad for this afternoon’s clash with Exeter City.