Tonje, selected 53rd overall by Utah in the 2025 NBA Draft, brings collegiate experience from Colorado State, Missouri, and Wisconsin. He earned All-American honors during his senior year at Wisconsin, averaging 19.6 points per game.
Previously playing for the Salt Lake City Stars in the G League, Tonje was traded to Boston in a deal involving Chris Boucher on February 5. After time with the Maine Celtics affiliate, the Celtics converted his deal to a 10-day NBA contract on February 19. He made his NBA debut on February 24 against Phoenix and scored his first career points with 2 against Brooklyn on February 27.