Färjestad BK (2006–2010)

In 2006–07, Johansson played for Färjestad BK's under-18 team and scored five goals with nine assists, with eight penalties-in-minutes (PIM), in 12 games. In eight playoff games, he scored seven goals with three assists. In Sweden's under-17 TV-pucken tournament, he played eight games for Skåne and had five goals with five assists, including 41 PIM.

In 2007–08, Johansson split his second season with the Färjestad between their U18 team and on loan to Skåre in Sweden's third division before making his Elitserien debut in the playoffs. Johansson went scoreless three games, however, in the SEL playoffs. In 19 games with Skåre's senior team, he scored two goals and ten assists. He also scored 12 goals with 26 assists for Färjestad's U18 team. In the U18 playoffs, he scored four goals with eight assists in eight games.

In the 2008–09 season, Johansson saw limited ice time in his first full season in the SEL, as Färjestad BK finished the regular season at the top of the league, and continued to win the playoff championships. He scored five goals with five assists and was +4 in 45 games while averaging just less than 10 minutes of ice time per game. In the playoffs, he played in six of the team's 13 games and was a –1, averaging 7:23 minutes of ice time. Johansson was also loaned again to Skåre in Sweden's third league, where he scored five goals with five assists in ten games with the club.

At the 2009 NHL Entry Draft, Johansson was selected 24th overall by the Washington Capitals. Remaining in Sweden for the 2009–10 season, Johansson moved from winger to center in his second year with Färjestads and saw increased playing time with the Karlstad-based club. His ten goals were tied for fourth on the team, and he added ten assists in 42 games while averaging just over 14 minutes of ice time per game. For the season, he finished with an even plus-minus and just 10 PIM. Färjestads slipped to fifth, however, in the 12-team league, and fell to Skellefteå AIK in a seven-game series in the first round of the playoffs. Johansson had five assists and was an even plus-minus in the playoffs. In May 2010, he signed a three-year, entry-level contract with the Capitals.

Washington Capitals (2010–2017)

Johansson (foreground) advances with the puck during the game in the 2017 Stanley Cup playoffs

On 17 May 2010, Johansson was signed to a three-year entry-level contract with the Capitals. He recorded his first NHL goal on 19 October 2010 against Tim Thomas of the Boston Bruins. In his rookie season, in 2010–11, Johansson was a regular in Washington's lineup, typically centering the second or third lines. He played an average of 14:43 in 69 games, netting 13 goals and 14 assists. Following the 2014–15 NHL season Johansson became a restricted free agent under the NHL Collective Bargaining Agreement. The Washington Capitals made him a qualifying offer to retain his NHL rights and, on 5 July 2015, Johansson filed for Salary Arbitration.^[3]

New Jersey Devils (2017–2019)

With the Capitals facing cap constraints, on 3 July 2017, Johansson was traded to the New Jersey Devils in exchange for second and third round picks in 2018.^[4] On 5 July 2017, the Devils announced that Johansson would become the second player in team's history to wear a number in the 90–99 range after he chose to wear number 90 on his uniform.^[5]

Boston Bruins (2019)

During the 2018–19 season, while in his final year under contract and with the Devils out of playoff contention, Johansson was dealt at the trade deadline on 25 February 2019, to the Boston Bruins in exchange for a second round pick in 2019 and a fourth round pick in 2020.^[6]

Johansson would find chemistry with Bruins forwards Charlie Coyle and Danton Heinen on the Bruins' third line during the 2019 Stanley Cup playoffs. Johansson and the Bruins would make it all the way the 2019 Stanley Cup Finals, where they were defeated by the St. Louis Blues in seven games.

Buffalo Sabres (2019–2020)

On 6 July 2019, the Buffalo Sabres signed Johansson a two-year, $9 million contract.^[7] In his lone season with the club, he recorded 30 points in 60 games.

Minnesota Wild (2020–2021)

On 16 September 2020, Johansson was traded to the Minnesota Wild in exchange for Eric Staal.^[8]

Seattle Kraken (2021–2022)

On 6 August 2021, Johansson was signed as a free agent to a one-year, $1.5M contract with expansion club, the Seattle Kraken.^[9] Johansson began the Kraken's inaugural 2021–22 season, on the injured-reserve. In returning to health, Johansson appeared in 51 regular season games, posting six goals and 23 points.

Return to Washington (2022–2023)

On 21 March 2022, with the Kraken out of playoff contention, Johansson was traded by the Kraken back to the Washington Capitals in exchange for forward Daniel Sprong, a 2022 fourth-round pick, and a 2023 sixth-round pick. The Kraken retained 50 percent of Johansson's $1.5 million cap hit.^[10]

Second stint with Minnesota (2023–present)

During the 2022–23 season, on 28 February 2023, Johansson was traded by the Capitals back to the Wild, in exchange for a third-round pick in 2024.^[11]