Johnson started off at Blackburn

The 22-year-old has signed a two-year contract and for an undisclosed fee.

Meanwhile, Wolves have extended 25-year-old goalkeeper Graham Stack's initial month-long loan spell from Reading until January.

American-born Johnson moved to England at the age of five and came through the ranks at Blackburn before a switch to Wolves in August 2006.

He struggled to make an impact at Molineux and was loaned out to Leeds, and had not featured for Wolves this season before his move.