Wahlstrom played for the
USA Hockey National Team Development Program in the 2016–17 and 2017–18 seasons, where he served as an alternate captain for the under-18 team in his final season. He originally committed to play for the
University of Maine when he was just 13 years old, becoming the first player born in the 2000s to commit to play
college ice hockey, as well as the youngest player ever to commit to play college ice hockey, before switching his commitment to
Harvard University for the 2018–19 season, and finally to
Boston College. In the
2018–19 season, Wahlstrom recorded 8 goals and 11 assists for 19 points as a freshman in 36 games. At the conclusion of the Eagles' season, Wahlstrom concluded his collegiate career by agreeing to a three-year, entry-level contract with the
New York Islanders on March 28, 2019. Wahlstrom made his NHL debut on October 14, 2019, against the
St. Louis Blues. On August 31, 2020, Wahlstrom was loaned by the Islanders to
AIK of the Swedish
HockeyAllsvenskan to start the 2020–21 season. He returned from his loan spell on December 14. Wahlstrom scored his first NHL goal on January 28, 2021, in the Islanders' 6–3 loss to the
Washington Capitals. His first multi-point game occurred on February 28, 2021, with a goal and an assist in a 2–0 win against the
Pittsburgh Penguins. Wahlstrom's first NHL playoff goal came on May 22, 2021, on the power play, at
Nassau Coliseum in a 4–1 win against the Penguins. On July 25, 2024, Wahlstrom signed a one-year contract extension with the Islanders to avoid
salary arbitration. In his sixth season in New York in , Wahlstrom registered just 2 goals and 4 points through 27 appearances before he was placed on waivers by the Islanders. On December 14, 2024, Wahlstrom was claimed off waivers by the
Boston Bruins. Wahlstrom made 16 appearances with the Bruins, posting 2 points, before he was reassigned and played out the remainder of his contract in the AHL with affiliate, the
Providence Bruins. As a free agent from the Bruins, Wahlstrom remained un-signed over the summer until he was signed to a one-year AHL contract with the San Jose Barracuda, affiliate to the
San Jose Sharks, for the
2025–26 season on September 16, 2025. ==Personal life==