On 20 June, he was named the recipient of the trophy, becoming the first player since Wayne Gretzky to win an end-of-season award in their team's inaugural season in the NHL. Karlsson was also awarded the Guldpucken as the top Swedish ice hockey player in the 2017–18 season. After his career-high season, on 4 August 2018, Karlsson signed a new one-year, $5.25 million contract with Vegas for the 2018–19 season. Karlsson described his decision to sign a one-year contract as "betting on [him]self a little" and that he would use the subsequent season to prove that his 2018–19 production "was no fluke". On 24 June 2019, having produced 24 goals and 32 assists (56 points) in the 2018–19 season, Karlsson signed a new eight-year, $47.2 million contract with Vegas worth an average annual value of $5.9 million. The contract is effective from the 2019–20 season through to the end of the 2026–27 season.