Staunton's relegation to second fiddle behind Ireland outhalf Ronan O'Gara and increased competition at 15 at Munster is believed to be his motivation for the move, where he will now battle it out for the number ten shirt with former Leinster outhalf Andy Dunne.
Quins also announced the signing of three other players including Wales and Lions utility back Dafydd James, England A prop Maurice Fitzgerald and young Bath winger Joe Mbu.
"We are delighted to welcome this group of players to the Stoop,"
"I'm confident all four will make a significant contribution to the squad." said NEC Harlequins Chief Executive Mark Evans.