Born in Graz, Styria, Wallner began his career with hometown Sturm Graz in 1998. In the following year he moved to Rapid Wien, where he would have his most successful years, appearing in over 100 matches and scoring 42 goals over five seasons with the club.
Wallner's football career started in Graz, Austria, with Sturm Graz in 1998. He then moved to Rapid Wien, where he had his most successful years, playing over 100 matches and scoring 42 goals during five seasons with the club.