Sweden Johnsson made his
Elitserien debut for
Frölunda HC on 18 December 2012 in a home game against
AIK IF. In his second game, on 26 December at
Rögle BK, Johnsson scored his first career Elitserien goal, the game-winning goal in the shootout. debut with
Frölunda HC in December 2012 On 21 April 2014, Johnsson was named the SHL Rookie of the Year, beating out Frölunda teammates
Alexander Wennberg and fellow Maple Leafs prospect
Tom Nilsson, as well as
HV71's
Kevin Fiala. During the
2014–15 season, Johnsson led Frölunda in goals with 22, also contributing 13 assists for 35 points from 55 regular season games played. On 4 June 2015, the Maple Leafs signed Johnsson to a three-year, entry-level contract.
NHL Toronto Maple Leafs The following season was another sensational year for Johnsson, in which he finished sixth in league scoring and helped Frölunda capture their fourth championship. Having stated this would be his last season in Sweden and wanting to begin his North American development, Johnsson debuted for the
Toronto Marlies—the Maple Leafs'
American Hockey League (AHL) affiliate—shortly afterwards in order to assist their Calder Cup playoff run. However, his stint was cut short, as in his second North American game, Johnsson was hit in the head by an elbow from
Albany Devils player
Dan Kelly. Kelly was suspended ten games for the play and Johnsson would not play another game that season. , participating in the 2018
AHL All-Star Game During the
2017–18 season, Johnsson was named to the 2018 AHL All-Star Game as a replacement for fellow Maple Leafs prospect
Kasperi Kapanen, who was called up to the NHL. On 13 March 2018, Johnsson was called up to the Maple Leafs alongside
Calle Rosén. He recorded his first NHL goal in the following game against the
Montreal Canadiens, a 4–0 victory. Johnsson recorded his first multi-point game on 2 April 2018 in a 5–2 win over the
Buffalo Sabres. Near the conclusion of the 2017–18 regular season, Johnsson was selected for the AHL's
Second All-Star team. Johnsson made his NHL playoff debut during the
2018 Stanley Cup playoffs against the
Boston Bruins and recorded his first playoff goal on 21 April to help the Leafs win 4–3. After the Leafs were eliminated from the playoffs, Johnsson was sent down to the Marlies to help them in their
2018 Calder Cup playoff run. After leading all players in points during the playoffs, Johnsson was awarded the Jack Butterfield Trophy as MVP of the Calder Cup. As a
restricted free agent entering the off-season, Johnsson accepted his
qualifying offer from the Maple Leafs, signing a one-year, two-way contract worth $787,500. Following a successful training camp, Johnsson began the
2018–19 season with the Maple Leafs in the NHL. On 24 November, in a game against the
Philadelphia Flyers, Johnsson scored his first career NHL
hat-trick by scoring three goals in the first period to lead the Leafs to a 6–0 win. On 28 June 2019, after scoring 20 goals and 43 points, Johnsson signed a new four-year, $13.6 million contract with the Maple Leafs worth an average annual value of $3.4 million. In the
2019–20 season, Johnsson scored eight goals and 21 points in 65 games with the Maple Leafs. His season came to an end after suffering a knee injury in a collision with teammate Kasperi Kapanen. On 19 February 2020, it was announced he would miss the rest of the season.
New Jersey Devils On 10 October 2020, Johnsson was traded by the Maple Leafs to the
New Jersey Devils in exchange for
Joey Anderson.
San Jose Sharks On 26 February 2023, Johnsson was included in a multi-player trade to the
San Jose Sharks in exchange for
Timo Meier.
Return to Sweden Signalling the end of his tenure in North America, Johnsson immediately returned to his native Sweden and rejoined the SHL by agreeing to a four-year contract with Skellefteå AIK on 10 November 2023. In joining the club he was reunited with his brother Jonathan. ==Career statistics==