Scowen, 24, who made his first-team debut at the age of 17 with Wycombe, joins on a free transfer having turned down a new contract with the Tykes.
Enfield-born Scowen played 44 games to help Barnsley to a 14th-placed finish in England's second tier last season.
He moved to the Oakwell club for an undisclosed fee in January 2015.
Find all the latest football transfers on our dedicated page.
Queens Park Rangers have signed midfielder Josh Scowen on a three-year deal following his exit from Championship rivals Barnsley.