2006-07: Simon Hjalmarsson played in two games with the second division Gisleveds SK men's team and was among the top players in Sweden junior hockey playing for the Frolunda U20 and U18 teams. He had one assist with Gislaveds SK and scored 54 points in 41 regular season games for the Frolunda U20 team— finishing the season with 31 goals, 23 assists and 91 penalty minutes. Hjalmarsson scored 1 goal with 1 assist and 6 penalty minutes in eight playoff games as Frolunda won the U20 championship. Hjalmarsson scored 3 goals with 8 assists and 2 penalty minutes in six playoff games as the Frolunda U18 team captured a silver medal. He played for the bronze medal-winning Sweden U18 team in the 2007 World Junior Championship and scored 4 goals with 5 assists, finishing +8 with 4 penalty minutes, in six games. Hjalmarsson was ranked sixth amongst international skaters in the CSS final rankings and was selected by St. Louis in the second round (39th overall) of the 2007 NHL Draft.
2007-08: Hjalmarsson began the season with Boras HC in the Sweden second league, Allsenskan, and appeared in one Elitserien game with Frolunda while again putting up points and penalty minutes with the Frolunda U20 team. He appeared in 13 international games skating for the Sweden U20 and U19 teams. Hjalmarsson made his Elitserien debut in March against MODO, playing three minutes and receiving a two minute penalty in his only action. In ten Allsvenskan games with Boras he scored 2 goals with 4 assists and was -2 with 4 penalty minutes. Hjalmarsson scored 16 goals with 30 assists and 104 penalty minutes in 37 games with the Frolunda U20 club during the regular season and scored 3 goals with 9 assists and 8 penalty minutes in eight playoff games as Frolunda repeated as champions. He was scoreless with 2 penalty minutes in four games for the Sweden U20 team and scored 5 goals with 3 assists and 2 penalty minutes in nine games for the Sweden U19 squad.
2008-09: Hjalmarsson spent the season with Boras HC in Allsvenskan — joining the Frolunda U20 team for the playoffs — and played for the Sweden U20 team in the 2009 World Junior Championship. He scored 14 goals with 19 assists in 40 regular season games for Boras HC and was +6 with 28 penalty minutes. Hjalmarsson scored 2 goals with 2 penalty minutes in two regular season games for the Frolunda U20 team and scored 8 goals with 2 assists and 2 penalty minutes in five playoff games. He scored 4 goals with 2 assists and was +6 with 4 penalty minutes as Sweden won a silver medal at the 2009 WJC. Hjalmarsson was not signed by St. Louis and re-entered the 2009 NHL Draft in June but was not selected.
2009-10: Hjalmarsson signed a two-year contract with Elitserien club Rogle Angelholm in May 2009 and skated in 53 of 55 regular season games and all ten Kvalserien games in his rookie season. He tied for second on the team with 11 goals and had nine assists, finishing minus-7 with 16 penalty minutes as Rogle finished last in the 12-team league. Hjalmarsson scored 4 goals with 5 assists and was +6 with 14 penalty minutes in 10 Kvalserien games. Rogle finished third in the six-team tournament and was relegated to Allsvenskan for 2009-10.
2010-11: Hjalmarsson was signed by Lulea in April after Rogle was relegated and moved to the club in northern Sweden for his second Elitserien season. He was the fifth-leading scorer for Lulea with 8 goals and 21 assists and was -8 with 16 penalty minutes; skating in all 55 regular season games. Lulea finished fourth and reached the playoff semifinals. Hjalmarsson scored 2 goals with 3 assists and was minus-2 with 2 penalty minutes in 13 playoff games. He saw his first action with the Sweden national team and in six games had no points with 2 penalty minutes.
2011-12: Hjalmarsson led Lulea with 19 goals and was the second-leading point scorer for the Elitserien club behind Niklas Olausson in his second season. He skated for Sweden in two of the four weekend tournaments in the Euro Trophy tournament against Finland, Russia ,and the Czech Republic. In 53 regular season games for Lulea he had 17 assists with his 19 goals and was +13 with 8 penalty minutes. Lulea finished first in the regular season but was upset by seventh-place AIK in five games in a best-of-seven quarterfinal series. Hjalmarsson scored 1 goal with 1 assist and was minus-1 with 4 penalty minutes in five playoff games. He scored 1 goal with 1 assist in 12 games for Team Sweden and was +1 with no points nor penalties in six games during the Euro Hockey Trophy tournament.
2012-13: Hjalmarsson moved from Lulea to Linkopings in his fourth Elitserien season and won a gold medal skating for Team Sweden in the 2013 IIHF World Championship. He scored 12 goals with 31 assists and was +21 with 10 penalty minutes in 55 regular season games, finishing third on Linkopings with 43 points. Linkopings finished fifth and topped HV71 in the quarterfinals before losing to Skelleftea in five games in the semifinals. Hjalmarsson scored 5 goals with 6 assists and was +5 with 8 penalty minutes in 10 playoffs games. In ten games at the World Championship he scored 2 goals with 2 assists and was +2 with 4 penalty minutes. Sweden defeated upstart Switzerland, 5-1, in the gold medal game.
2013-14: Hjalmarsson was among the league leaders in points and penalty minutes in the re-christened SHL in his second season with Linkopings. He scored 27 goals (three behind league leader Chad Kolarik) with 30 assists (tied for fourth) and had an even plus/minus with 87 penalty minutes (fourth most) while skating in all 55 regular season games. Linkopings finished ninth in the regular season but reached the playoff semifinals in the expanded SHL playoffs. Hjalmarsson scored 5 goals with 4 assists and was minus-1 with 2 penalty minutes in 14 playoff games. He was an assistant captain for Sweden during the Euro Hockey Trophy tournament, scoring 2 goals with 3 assists in nine games and won a bronze medal skating for Sweden in the 2014 IIHF World Championship in Belarus. In ten games he scored 1 goal and was minus-3 with 4 penalty minutes. Hjalmarsson signed a one-year entry-level contract with Columbus on June 4th, 2014.
A very well-rounded player, Hjalmarsson stands out with his speed, technical skills and intensity. He's a good goal scorer with a quick release and above average playmaking ability who has so far produced at all levels. Although he has plenty of flash offensively, Hjalmarsson is also a hard worker with excellent attitude and penalty killing ability. He needs to become stronger.
Hjalmarsson signed a one-year deal with the Columbus Blue Jackets for the 2014-15 season.