Gallagher made his debut performance as a substitute in a 2–0 win over the 2001–02 Premier League champions Arsenal on 15 March 2003, as a replacement for Dwight Yorke.

On 21 February 2004, in an away game against Charlton Athletic, Gallagher assisted goalkeeper Brad Friedel to his only career goal from open play in the 90th minute.

Against Southampton on 15 April 2006, he exchanged a one-two on the edge of the area with Adam Rooney before drilling home a thunderous thirty-yard drive into the far top corner of the net.

[7] On transfer deadline day 31 August 2007, Gallagher signed a six-month loan deal with Championship side Preston North End, after being linked with a return to Stoke.

"[11] On 30 August 2008, Gallagher signed on loan for the rest of the 2008–09 season with Plymouth Argyle,[12] making his debut that same day at Turf Moor against Burnley.

Although Blackburn Rovers appointed Sam Allardyce as their new manager in December 2008,[13] Plymouth was allowed to keep Gallagher for the remainder of his loan.

[25] On 12 March 2011, Gallagher provided three assists as Leicester beat Scunthorpe 3–0 at Glanford Park,[26] earning praise from manager Sven-Göran Eriksson, who believed "he is not far from Beckham in terms of his delivery of set-pieces.

[34] He played 59 times for North End in 2014–15 scoring 13 goals as they gained promotion after beating Swindon Town 4–0 in the play-off final.

[40] Gallagher oversaw two EFL Championship draws against Swansea City and West Bromwich Albion before he reverted to first-team coach under new manager Steven Schumacher.

[42] Gallagher's form for Blackburn Rovers in January 2004 impressed Berti Vogts, then manager of Scotland, who described him as "very quick, strong and with good body movement.