2006-07: Drafted in the first round (6th overall) of the 2007 WHL Bantam Draft by the Lethbridge Hurricanes.
2007-08: Theriau received his first WHL action, appearing in 4 games for the Lethbridge Hurricanes. He picked up no points and 2 penalty minutes in those games.
2008-09: In his WHL rookie season, Theriau played for two clubs, the Lethbridge Hurricanes and the Everett Silvertips. In 29 games for the Hurricanes, he notched 4 assists for 4 points to go along with 17 penalty minutes. Theriau was traded to the Silvertips in the deal that brought Kyle Beach to the Hurricanes. He played in 26 games for the Silvertips, scoring 1 goal for that club. In 55 total games, Theriau had 1 goal and 4 assists for 5 points. He played in one playoff game for the Silvertips but did not register a point.
2009-10: In 70 games for the Everett Silvertips, Theriau 4 goals and added 20 assists. He added 68 penalty minutes and was a +12 for the season. In 7 playoff games, Theriau picked up 2 assists. he was named the Silvertips Most Improved Player for 2009-10.
2010-11: Alex Theriau was traded for the second time in his junior career in 2010-11. This time he was shipped from Everett to Medicine Hat. After just seven assists in 37 Silvertips games, Theriau had a veritable offensive explosion in “The Hat” – a goal and eight helpers in 15 contests. He also notched his first career playoff goal (plus five assists) in Medicine Hat’s trek through the Western League playoffs. The Duncan, BC native scaled down the pugilistic portions of his game a bit this year and, naturally, his penalty minutes dropped by more than half.
Heady defenseman that plays a cool, smart game. Has a fine stride but isn’t terribly quick. Has a pretty good defensive game, though it’s a bit tentative. His gaps are usually fairly relaxed and allows the forward to make the mistake as opposed to forcing one himself. Surprisingly willing combatant to stand up for teammates in fights, but that has cooled off as he’s gotten older. Likes to get pucks to the net. Pretty average at everything.
Theriau was not signed by the Stars, nor was he chosen at the 2012 NHL Draft.