The ex-Blackburn Rovers striker has also played for Preston and Darlington on loan, before leaving Ewood Park to join Wolves for an undisclosed fee last summer.
Johnson has scored only three goals in 24 appearances for Wolves this season.
Following the January signings of former Leeds forward Andy Keogh and Stephen Ward, Johnson is now out of the first team picture.
Wolves boss Mick McCarthy told his club's website: "Leeds expressed some interest before. Dennis wants to freshen up his squad so this will be a good move for him."