Horák began his professional career with his hometown team HC České Budějovice of the Czech Extraliga, appearing in one game with the club in 2007–08 and eight more in 2008–09.

[7] However, before he played a game with the NHL team, he was traded to the Calgary Flames on June 1, along with two draft picks, in exchange for defenceman Tim Erixon.

[11] On November 8, 2013, Horák was traded to the Edmonton Oilers alongside goaltender prospect Laurent Brossoit in exchange for Ladislav Šmíd and minor league goalie Olivier Roy.

With his NHL rights still owned by the Oilers, Horák opted to return to Europe by signing a one-year contract with Russian club Vityaz Podolsk of the Kontinental Hockey League (KHL) on May 12, 2014.

[13] Horák played two seasons in the Swedish Hockey League with the Växjö Lakers before opting to return to his native Czech Republic as a free agent.