Thomsson began his football career at Mörbylånga GoIF, before joining as a young player to Kalmar FF. After four years at the club, he moved in 1994 to the fifth-tier Färjestadens GoIF further, with whom he marched through within two years in the third league. Although he missed with the team at the end of the 1996 there in the league, he remained at the league level and returned to Kalmar FF, which was relegated from the second division. With the club he managed again a walkthrough of two leagues, as the return to the second division was accomplished without loss of the season in which the team then finished the Südstaffel as the leader with one point ahead of Landskrona BoIS. Under coach Nanne mountain beach he was together with Johan Paulsson with seven goals this season best club internal Totschütze, after a 1-1 draw and a 1-2 defeat against the Gothenburg club GAIS in the relegation games he missed, however, with the team in the Premiership season 1999 in the league.
In early 2001 Thomsson moved to Norway. For Sandefjord Fotball, he played one season in the Adecco Ligaen. At the second division season 2002 he returned to Sweden and joined Åtvidabergs FF. By 2004, he ran on for the club in the second division, before he ended his active career in the summer of the year to take over as coach at the fourth division Linköping FF. With last year's relegation, he finished at the end of the last non- relegation zone. In the following season he was with the team in a league reform at the fourth level of play.
2006 Thomsson returned to Åtvidabergs FF, where he took over the Assitenztrainerposten under coach Kent Karlsson. In parallel, he became involved in the image Happenings Centrum facets as a physical education teacher and head of the football field. As at the end Karlsson left the club, he remained active in the same capacity under the newly obligated Peter Swärdh. With the club, the two reached two consecutive sixth place in the Superettan before Swärdh accepted an offer of league rivals Mjallby AIF following the 2008 season in late October. Briefly brought by the press as the successor to the conversation, he rejected this with reference to his strong role as an assistant and his work on the sports school. So he stayed in the background and assisted the new coach Daniel Wiklund. With the team around players like Pontus Karlsson, Daniel Hallingström, Jesper Arvidsson and Kristian Bergström, the club finished second in the second division season 2009 Mjallby AIF behind in second place and was promoted to the Allsvenskan.
At the start of the Premiership season 2010 Åtvidabergs FF conceded three defeats in a row and remained without a goal. Then, the club parted the end of March of Wiklund and appointed Thomsson his successor. After the descent of the club to the end of the season he remained in office and went with the team right back on. This time, succeeded as eighth in the league table.
Despite the success Thomsson left the club and joined the beginning of December 2012 the Erstligaaufsteiger Östers IF to, in which he replaced the to Helsingborgs IF migrated Roar Hansen and signed a two -year contract with an option for another season.