Career
Before playing in the NHL, Middleton played one season with the Owen Sound Attack and four seasons with the Ottawa 67's of the Ontario Hockey League (OHL).
He was drafted 210th overall by the Los Angeles Kings of the 2014 NHL entry draft. He never played a game for the Kings.
On April 8, 2016, Middleton signed a try-out agreement with the Manchester Monarchs of the ECHL. He recorded 1 assist in 2 regular season games with the Monarchs. On September 7, 2017, Middleton signed a three-year, $2.205 million entry-level contract to join the San Jose Sharks. He was sent down to play for their AHL-affiliates San Jose Barracuda.
On January 5, 2019, the Sharks called him up and Middleton made his NHL debut in a 5–2 win against the Tampa Bay Lightning. On April 4, he recorded his first NHL point after assisting on a Marcus Sörensen goal in a 3–2 win against the Edmonton Oilers. On November 24, 2021, Middleton scored his first NHL goal on an empty net in a 6–3 win against the Ottawa Senators.
On March 21, 2022, the Sharks traded Middleton to the Minnesota Wild in exchange for Kaapo Kähkönen and a 2022 fifth-round draft pick. On July 6, Middleton signed a three-year, $7.35 million contract to stay with the Wild. On July 6, Middleton signed a four-year, $17.4 million contract to stay with the Wild.
On July 2, 2026, the Wild traded Middleton along with a 2029 second-round draft pick, 2027 third-round draft pick, and a 2028 fourth-round draft pick to the Calgary Flames in exchange for Blake Coleman and Olli Määttä.
Canada