In his junior season at Northeastern, Thiessen was named Hockey East Player of the Year, a conference all-star, an NCAA first-team All-American, and a Hobey Baker Award "hat trick" finalist.

At the end of the 2008–09 season, Thiessen signed a contract with the Pittsburgh Penguins as an undrafted free agent.

He was included on the team picture, and awarded a Stanley Cup ring before playing his first pro game.

[5] On his 25th birthday, he became the third Penguins goaltender to record 30 wins in a single season, joining Dany Sabourin (2005–06) and John Curry (2007–08).

On March 24, 2011, Thiessen was recalled by the Pittsburgh Penguins[6] due to an injury to backup goalie Brent Johnson, but did not play in an NHL game.

On July 15, 2013, Thiessen opted to leave North America and signed his first European contract with HIFK of the Finnish Liiga.

[8] At the tail end of the season, on April 5, 2015, Thiessen was called up by the Calgary from the Adirondack Flames and served as backup without making his debut for the club.

On September 23, he was reassigned by the Blue Jackets to attend AHL affiliate, the Lake Erie Monsters, training camp.