Under the guidance of coach Mihailo Pavićević, he quickly developed into a key component of Honka's Finnish League championship-winning side in 2006–07.

He recorded 7 points and 6 assists with only one turnover, playing against future NBA super star, MVP Derrick Rose.

In the first game of December, Koponen played through a concussion and led the Honka Playboys to an overtime victory over Team Componenta, scoring 32 points, grabbing six rebounds and dishing out five assists.

[citation needed] On 14 July 2008, in the NBA Summer League game against the Washington Wizards, Koponen scored 19 points, shooting 4-for-6 on three-point attempts.

[9] On 24 July 2018, Koponen signed a three-year contract with Bayern Munich of the German Basketball Bundesliga (BBL).

Philadelphia then traded Koponen to the Portland Trail Blazers in exchange for Derrick Byars and cash considerations.

[20] Koponen joined the coaching staff of the San Antonio Spurs for the 2024 NBA Summer League.

[20] On 4 July 2024, Koponen was named the head coach of the New Zealand Breakers in the Australian National Basketball League (NBL) on a two-year deal.