The U.S. international midfielder will stay with the Championship side for two more months before he returns to the Premier League's Stoke City.
The American's loan was originally a 28-day deal but now will last through April 3, which gives him the opportunity to play in 14 more games.
Shea has made just two first-team appearances since joining Barnsley earlier this month. He made his debut on New Year’s Day against Birmingham and earned another start on Jan. 18 against Blackpool.
The winger is one of three U.S. internationals to be loaned by the Premier League club this season. Juan Agudelo was loaned to FC Utrecht last week and Maurice Edu finalized a loan move with the Philadelphia Union on Monday.