He started with Kuusysi Lahti and soon raised the interest of European top teams. In 2000 he went to Ajax Amsterdam and became a regular player in the first squad. In August 2001 he broke his leg and missed most of the 2001/02 season. After his injury he came back to the team. With Ajax he reached the quarterfinals of the UEFA Champions League in the 2003/04 season. During the second half of the 2003/04 season he was on loan at English club Portsmouth in the Premier League. Portsmouth manager Harry Redknapp was interested in buing Pasanen at the end of the season, but the price was to high. So Pasanen signed with SV Werder Bremen in the German Bundesliga. After the end of his contract on 30 June 2011 he left Werder Bremen and signed for Red Bull Salzburg in the Austrian Bundesliga. He became a regular player from the beginning.