He was selected by the Rangers in the 6th round (168th overall) of the 2007 NHL Entry Draft.
Prior to beginning his college career, he played two seasons for Södertälje’s team in the J20 SuperElit. During that time he scored 44 goals and 51 assists, and ranks 5th all time in points and goals for Södertälje, as well as 4th in goals per season.
Hagelin played college hockey for the Michigan Wolverines of the Central Collegiate Hockey Association (CCHA). He is the first Swedish ice hockey player to play for Michigan. As a junior in 2009-10, Hagelin helped Michigan win the CCHA championship and was Academic All-Big Ten. As a senior in 2010-11, besides winning the CCHA Best Defensive Forward Award, he was named to the All-CCHA first team. He won the CCHA Best Defensive Forward Award and was a finalist for the CCHA Player of the Year Award for the 2010-11 season. Hagelin was named to the Inside College Hockey 2010-11 All-America Third Team and the AHCA/Old Time Hockey All-American Ice Hockey Team (second team, west). He was a sixth round draft choice of the New York Rangers in the 2007 NHL Entry Draft.
Hagelin played in the 2008 World Junior Ice Hockey Championships with Sweden and won silver. The Rangers signed Hagelin to a professional contract after Michigan lost the 2011 NCAA final game, and he joined the Rangers’ AHL affiliate the Connecticut Whale for the 2011 AHL playoffs. He also began the 2011-12 season playing for the Whale.
Hagelin made his NHL debut against the Washington Capitals on November 25, 2011, registering an assist on a goal byBrian Boyle for his first NHL point. He scored his first NHL goal the next day against Sergei Bobrovsky of thePhiladelphia Flyers.
After Adam Henrique of the New Jersey Devils pulled out of the 2012 NHL All-Star Rookie Showcase due to injury, Hagelin took his spot and was slated to take part in the fastest skater challenge during the Skills Competition. Hagelin won the competition by beating Ottawa Senators rookie Colin Greening with the fastest final round time ever recorded. Nevertheless, Hagelin later admitted Rangers teammate Marian Gaborik may be an even faster skater.
On April 15, 2012, Hagelin received a three-game suspension for elbowing Ottawa Senators captain Daniel Alfredsson in the head during New York’s loss in Game 2 of the first-round Eastern Conference playoff series.