Career
Before playing in the NHL, Karlsson played two seasons with HV71 of the Elitserien/Swedish Hockey League (SHL). He had a successful time with HV71. He finished his rookie season scoring 4 goals and recording 24 assists for 28 points in 50 regular season games. He was named the SHL Rookie of the Year for his effort. He was also awarded the Guldpucken for being the SHL's player of the year.
He was drafted 53rd overall by the Anaheim Ducks in the 2011 NHL entry draft. On 20 May 2013, Karlsson signed a three-year, $2.4925 million entry-level contract to join the Ducks. He was sent down to play for their AHL-affiliates Norfolk Admirals.
On 11 October 2014, the Ducks called him up and Karlsson made his NHL debut in a 3–2 win against the Detroit Red Wings. Two days later on 13 October, Karlsson scored his first two NHL goals against Michal Neuvirth in a 5–1 win against the Buffalo Sabres.
On 8 March 2024, the Ducks traded Karlsson along with Rene Bourque and a 2015 second-round draft pick to the Columbus Blue Jackets in exchange for James Wisniewski and a 2015 third-round draft pick. On 23 June 2016, Karlsson signed an two-year, $2 million contract to stay with the Jackets.
On June 21, 2017, the Blue Jackets left Karlsson unprotected and he was drafted by the Vegas Golden Knights in the 2017 NHL expansion draft. On 31 December, Karlsson recorded his first hat-trick in a 6–3 win against the Toronto Maple Leafs. It was also the first hat-trick in Golden Knights franchise history. On 4 August 2018, Karlsson signed a one-year, $5.25 million contract to stay with the Knights. On 24 June 2019, Karlsson signed an eight-year, $47.2 million contract to stay with the Knights. He helped the Knights during the playoffs. They defeated the Winnipeg Jets, Edmonton Oilers, and Dallas Stars. They went on to defeat the Florida Panthers four games to one in the Final to win the first Stanley Cup in Golden Knights franchise history.
Sweden