The 21-year-old Senegalese, who played in Arsenal's 8-2 hammering at Manchester United on Sunday, has signed a three-year deal at Loftus Road, QPR said in a statement.
Traore follows midfielder Joey Barton, signed from Newcastle United, and former Aston Villa defender Luke Young to the west London club who were taken over by Malaysian entrepreneur Tony Fernandes earlier this month.
"When I talked to [manager] Neil Warnock he was very passionate about what I could bring to the club," Traore, who made 33 appearances for Arsenal since signing in 2006 and spent time on loan at Juventus, said in a club statement.
"He was very motivated about playing me week in, week out, and that's what I need at this stage of my career."
Warnock, who led QPR back to the top flight for the first time since 1996, said Traore would benefit from playing regular first team football.
"Armand has been my number one defensive target for a while now. I've been speaking to [Arsenal manager] Arsene [Wenger] for a couple of weeks," Warnock said.
"He's a young and exciting lad who I think can only get better playing for a side like ourselves on a regular basis. He needs games and he'll get that here."
