Tomas started football in the youth sector of local club Ilves. After debuting in top-tier Veikkausliiga with Ilves first team in 2015, he spent a brief loan spell with Mikkelin Palloilijat (MP) in the third-tier Kakkonen in early 2016. He made a further three appearances in the league after his return to Ilves, and joined FC Haka for the 2017, competing in second tier Ykkönen.[3]
Tomas returned to Ilves at the start of 2018, and eventually spent three seasons with the club. Tomas won the 2019 Finnish Cup title with Ilves, and represented the club twice in UEFA Europa League qualifiers.[3]
In early 2021, he joined fellow Veikkausliiga club KuPS on a two-year deal. During his time with KuPS, the club won two Finnish Cup titles, and finished in the 2nd place in the league twice.[5]
After playing for KuPS,[6] Tomas signed for Norwegian Eliteserien club Odds Ballklubb (Odd) in March 2023 on a one-year deal.[7] While in Norway, Tomas lived temporarily in a caravan in a forest,[8][9] and became a fan favourite cult figure[10] for his playing style and his personal hair style.[11] After the last match of the season, he donated parts of his mullet hair to the supporters.[12]
Following the expiration of his contract with Odd, Tomas refused a contract extension and returned to Finland after signing with reigning champions HJK Helsinki for the 2024 Veikkausliiga season.[13][14][15] He debuted with his new club in the league on 11 April 2024, as a substitute to Joona Toivio, in a 4–0 home win over FC Lahti.[16][17] On 29 August, in the 2nd leg of the UEFA Conference League qualifying play-off round, Tomas scored a goal against KÍ Klaksvík, helping HJK to win the pair 4–3 on aggregate and to qualify for the league phase.[18]