Furlong has made five appearances for QPR, but has not featured for them in a league match since a 3-1 Premier League defeat by Crystal Palace in March 2015.
The 20-year-old spent time on loan at Cambridge and Northampton last season, playing a total of 31 League Two games.
He could make his debut for Swindon when the Robins travel to Chesterfield in League One on Saturday.
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League One side Swindon have signed Queens Park Rangers defender Darnell Furlong on a season-long loan deal.