A native of Finland's capital city ofHelsinki, Söderholm played in the HIFKyouth system in the early- and mid-1990s before taking his game to North America. From 1995 to 1997, he attended Trinity College School in Ontario, then returned to HIFK for the 1997–98 season and headed over the pond again to enroll at the University of Massachusetts. He served as team captain for the Minutemen his senior year. Upon graduation, Söderholm returned to HIFK and received LiigaRookie of the Year honors in the 2002–03 season. In his second year in the league, Söderholm won the Pekka Rautakallio Award as the Defenceman of the Year. After his third season, in which he served as HIFK captain, he took up an offer from Switzerland and embarked on a two-year stint with SC Bern of the National League A in 2005. Söderholm then signed with Frölunda HC of the Swedish Hockey League in 2007. In the course of the second season with Frölunda, he returned to HIFK. Söderholm won the Finnish championship with HIFK in 2011 and was presented with the Jari Kurri Award as the MVP of the playoffs. On April 7, 2015, after a total of 10 seasons with HIFK's men's team, Söderholm left abroad for a second time in his professional career in signing to provide a veteran presence on a one-year contract with German club EHC München of the Deutsche Eishockey Liga. He won the German championship in his single season with the München team and announced the end of his playing career some weeks later in May 2016.
In June 2016, a couple of weeks after he put an end to his playing career, Söderholm was named development coach of EHC München of the German top-flight Deutsche Eishockey Liga. In May 2017, he took over the head coaching job at SC Riessersee, München's affiliate in Germany's second-tier league DEL2. He guided SCR to the DEL2 finals in spring 2018, where they lost to Bietigheim. Söderholm earned DEL2 Coach of the Year honors for the 2017–18 season. SCR had to file for insolvency and therefore was relegated to the Oberliga before the start of the 2018–19 campaign. However, Söderholm stayed on the job. On December 20, 2018, Söderholm was named the new head coach of the German men's national team.
Teams
SC Riessersee, DEL2.
German men's national team, IIHF World Championships: 2019.
Honours and accolades
Won the Finnish SM-liiga Champion in 2010–11 season.
Won the Deutsche Eishockey Liga champion in 2015–16 season.