The 29-year-old Scotland international heads back to Deepdale after spending most of the 2013/14 campaign with the Lancashire club, under the management of former Foxes defender Simon Grayson.
After joining the Lilywhites in October, Gallagher made 35 appearances and scored 10 goals in all competitions, as Preston reached the League 1 play-offs only to be eliminated by eventual winners Rotherham United at the semi-final stage.
Gallagher’s latest loan agreement will run for the duration of the 2014/15 season and he will be eligible for selection in all league and cup competitions.