Career
He is currently playing with Severstal Cherepovets of the Kontinental Hockey League (KHL). He was selected by the New York Islanders in the 4th round (102nd overall) of the 2008 National Hockey League Entry Draft. On June 1, 2010, Ullström was signed by the New York Islanders to a three-year entry-level contract.
On December 6, Ullström scored his first National Hockey League goal against Mathieu Garon of the Tampa Bay Lightning.
On June 18, 2013, Lokomotiv Yaroslavl signed Ullström to a contract for the 2013-2014 season. Scoring just 3 goals in 18 games with Lokomotiv, Ullström transferred to The Human Context Lev Praha for the remainder of the campaign.
Establishing a scoring presence within Praha, he helped the club advance to the Gagarin Cup finals. On June 25, 2014, Ullström opted to remain in the KHL, signing for his third club, Severstal Cherepovets on a two-year deal.