As a result of his outstanding junior play, Severson was a ninth-round pick of the Kelowna Rockets in the 2009 WHL Bantam Draft.

As such, he won the Rockets' Most improved player and was selected by the New Jersey Devils in the second round of the 2012 NHL Entry Draft.

Prior to the start of the 2020–21 season, Severson was promoted to the rank of alternate captain by new head coach Lindy Ruff.

Severson made his senior team debut during the 2019 IIHF World Championship where he helped them clinch a silver medal.

As a result of his outstanding junior play, Severson was a ninth-round pick of the Kelowna Rockets in the Western Hockey League (WHL) 2009 bantam draft.

[6] After recording four goals and seven assists for 11 points through 32 games, Severson was named to Team West at the 2011 World U-17 Hockey Challenge.

[11] Following the signing, Severson and teammate Colton Sissons were not asked to attend their NHL teams' training camp and returned to the Rockets.

[13] As the season concluded, Severson signed an Amateur Tryout Agreement with the Albany Devils of the American Hockey League (AHL) and played two games.

[14] He then spent the offseason in his home province with a personal trainer before being selected for Team Canada's World Junior summer development camp.

[17] Upon returning for the 2013–14 season, Severson and teammates Myles Bell and Tyson Baillie were named assistant captains for the Rockets on November 1, 2013.

[22] After attending the Devils' 2014 rookie and training camp,[23] Severson cracked the NHL roster prior to the start of the 2014–15 season.

[26] Prior to his debut, Greene spoke highly of Severson, saying: "He's very mobile, makes a lot of great plays, can skate like the wind and is very confident."

[27] Two days later, he scored his first career NHL point, an assist, against the Florida Panthers and later recorded his first goal in the same game, six minutes later.

[46] On January 15, 2018, Severson helped the Devils end a six-game losing streak by scoring two goals in a 4–1 win over the Rangers.

[56] As he continued to produce, Severson's time on ice increased to a season-best 24:18[57] and he became one of only two Devils players to compete in all 82 games of the season.

[58] During the 2019 offseason, Severson competed with Team Canada at the 2019 IIHF World Championship and played in a charity softball game.

[59] Severson returned from the 2019 IIHF World Championship after helping Team Canada win a silver medal after a 3–1 loss to Finland.

[60] Although he split his offseason time between the tournament and training back home in Kelowna, Severson expressed his excitement for the moves Devils General Manager Ray Shero made during the summer.

[64] Prior to the start of the 2020–21 season, Severson was promoted to the rank of alternate captain by new head coach Lindy Ruff.

[67] Following the trade of Kyle Palmieri and Travis Zajac to the New York Islanders, Severson became the longest-tenured player on the roster at the age of 26.

[72] On June 9, 2023, after signing an eight-year extension with New Jersey, Severson was traded to the Columbus Blue Jackets in a sign-and-trade deal in exchange for a third-round pick in the 2023 NHL Entry Draft.

[75] On April 29, 2019, Severson was selected to make his senior international debut after he was named to Canada's roster for the 2019 IIHF World Championship held in Slovakia.

[76] On May 23, in the quarterfinal game against Switzerland, Severson scored the game-tying goal for Canada with 0.4 seconds left to play in regulation time.