Prior to the 2009 World Baseball Classic, Teahen, whose father was born in St. Marys, Ontario, became a naturalized Canadian citizen and played for Team Canada in that event.

Although he had been one of the most highly regarded prospects in the Oakland organization, he became available when the Athletics were able to sign Eric Chavez to a long-term contract.

Royals management did not expect Teahen to make the opening-day roster in 2005; however, after hitting .344 in spring training and after injuries sidelined potential third basemen Chris Truby and Chris Clapinski, the Royals announced Teahen would be their regular third baseman for 2005, and he made his major-league debut on April 4, 2005.

[3] While in Kansas City, Teahen was a spokesman and fundraiser for a program that gave children with physical or mental challenges the chance to play baseball.

Since Teahen obtained dual Canadian-American citizenship in 2005,[4] he was able to play for the Canadian team in the 2009 World Baseball Classic.

On November 5, 2009, Teahen was traded by the Royals to the Chicago White Sox in exchange for infielders Chris Getz and Josh Fields.

[8] On July 27, 2011, Teahen was traded to the Toronto Blue Jays with Edwin Jackson for Jason Frasor and Zach Stewart.

In his one season with the Blue Jays, Teahen played in 27 games, mostly as a pinch hitter and defensive replacement, and hit .190 with one home run and three RBI.

[10] The Texas Rangers signed Teahen to a minor league deal on May 23, 2013,[11] [12] and assigned him to the Triple-A Round Rock Express.