Undrafted, Smithson played in the
Western Hockey League with the
Calgary Hitmen before he signed his first NHL contract as a free agent with the
Los Angeles Kings. Smithson scored the game-winning goal for the
Nashville Predators in Game 5 of the
2011 Stanley Cup Playoffs quarterfinals to beat the
Anaheim Ducks 3-2. The Predators went on to defeat the Ducks in 6 games to preserve their first ever playoff series win. On February 24, 2012, Smithson was traded by the Predators to the Florida Panthers for a 2012 sixth round draft pick. April 3, 2013 he was acquired by the
Edmonton Oilers from the
Florida Panthers in exchange for a fourth round pick in the 2013 Draft. As a free agent leading into the
2013–14 season, Smithson signed a professional try-out contract with the
Toronto Marlies of the
American Hockey League on October 16, 2013. After 7 games with the Marlies, on November 6, 2013, Smithson returned to the NHL in signing a one-year contract with parent club, the Toronto Maple Leafs. Smithson later made his Leafs debut on November 8, 2013. Smithson was waived by the Maple Leafs on December 4, 2013, and after clearing waivers reported to the
AHL Toronto Marlies. After sitting out the 2014–15 season as a free agent, Smithson announced a comeback to professional hockey in agreeing to a one-year contract with Danish club,
Herning Blue Fox of the
Metal Ligaen on July 25, 2015. In his solitary season abroad in
2015–16, Smithson contributed with 24 points in 33 games, helping the Blue Fox to the finals in the post-season with 7 points in 19 playoff games. He announced his retirement from professional hockey following the season. ==Career statistics==