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.

[10] 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.

[11] On July 25, 2024, Wahlstrom signed a one-year contract extension with the Islanders to avoid salary arbitration.

[12] In his sixth season in New York in 2024–25, Wahlstrom registered just 2 goals and 4 points through 27 appearances before he was placed on waivers by the Islanders.

[17] Wahlstrom scored a highlight goal at age nine during a shootout contest before a Boston Bruins game in 2009.