A Shepherds Bush native, Gallen established himself as something of a legend with Queens Park Rangers. He notched up over 400 appearances and hit 97 goals for the R's in two spells spanning nearly 14 years.
Gallen joined Huddersfield 2000 and after 10 goals in 30 starts for the Terriers, Gallen moved across Yorkshire to join Barnsley the following summer, but the call of West London saw him return to QPR within a few months. He scored nine goals in 16 league starts for MK Dons before joining Luton on loan.
After a successful loan spell Gallen joined permanently in January 2009, signing until the end of the season before agreeing a one year contract extension with the club in May keeping him at Kenilworth Road until June 2010.