The 29-year-old joined City from Blackburn Rovers in the summer of 2009 and has since made 139 appearances for the Club, scoring 28 goals in the process.
Gallagher heads to Simon Grayson¹s promotion-chasing Lilywhites ahead of their weekend clash with struggling Tranmere Rovers at Deepdale - a stadium that will be familiar to Gallagher after his 19-game loan spell there during the 2007/08 campaign.
Last season saw Gallagher make 10 appearances for Nigel Pearson¹s side, most recently in a 2-2 draw away at Crystal Palace in April. He also had a brief loan spell with Sheffield United in League 1.