Gaardsøe most notably won the 1999 Danish Superliga with Aalborg Boldspilklub, and played abroad for English clubs Ipswich Town and West Bromwich Albion.
His name first caught the headlines when he was a part of the winning team in the 1994 and 1995 editions of the Danish nationwide school football tournament, scoring in both finals.
Despite occasional good performances, he had a hard time forcing his way into the AaB starting line-up in his role as central midfielder.
In the summer 2001, he was sold to English club Ipswich Town in the FA Premier League championship in a transfer deal worth £1.3 million.
Gaardsøe was an ever-present in Albion's promotion winning team and he was named "Player of the Year" by the supporters who, in turn, dressed up as Vikings in his honour for the away match at Reading on 1 May 2004.
[4] However, Gaardsøe did not succeed in establishing himself in the AaB squad and, in order to find regular first team football, he signed a contract with Danish superliga rivals Esbjerg from January 2010.