He missed two games while participating with Team USA in the IIHF World Junior U20 Championship in Canada which resulted in Thompson earning his second Gold Medal.

[3] After the completion of the Huskies season, Thompson opted to conclude his collegiate career and signed a three-year, entry-level contract with the St. Louis Blues on March 7, 2017.

[4] He immediately joined the Blues affiliate, the Chicago Wolves of the AHL, on an amateur try-out contract for the remainder of the 2016–17 season.

[9] On October 5, 2020, as a restricted free agent, Thompson signed a three-year, $4.2 million contract extension with the Sabres.

On December 7, against the Columbus Blue Jackets, he scored five goals in a game including four in the first period, becoming the fourth player in NHL history to do so.

[15] In January 2023, he was named to the 2023 NHL All Star Game, the first of his career, but would be replaced by defenseman Rasmus Dahlin due to injury.

[16][17] On February 23, Thompson became the first Sabres player to record four hat-tricks in a season since Drew Stafford in 2010–11, doing so in a 6–5 overtime win versus the Tampa Bay Lightning.

[18] Three days later, on February 26, he scored in a 7–4 win against the Washington Capitals, becoming a 40-goal scorer for the first time in his career, and the first player to do so for the Sabres since Jeff Skinner in 2018–19.