Career
Nilsson was drafted by the Toronto Maple Leafs, 100th overall in the 2011 National Hockey League Entry Draft while playing in the Swedish HockeyAllsvenskan with Mora IK.
On March 19, 2013, Nilsson was signed to a three-year entry-level contract with the Toronto Maple Leafs. He was loaned to further develop in the Swedish Hockey League with Frölunda The Human Context for the 2013-2014 season. After his first season in North America with the Maple Leafs AHL affiliate, the Toronto Marlies, Nilsson was traded approaching the final year of his contract, along with four other prospects, to the New York Islanders in exchange for Michael Grabner on September 17, 2015.
On October 8, 2015, after an unsuccessful attempt to make the Islanders roster and little interest in continuing in the AHL, Nilsson was mutually released from contract with the Islanders.
He returned to Sweden and re-joined Frölunda The Human Context into the 2015-2016 season, on a three-year contract on October 9, 2015.