On 23 February 2018, the Penguins traded Gustavsson to the Ottawa Senators (alongside Ian Cole, a 2018 first-round pick, and a 2019 third-round pick) in exchange for Derick Brassard. On 23 March 2018, Gustavsson was assigned to the Senators AHL affiliate, the Belleville Senators, after the conclusion of the SHL season.