Figures include both Episode One and Season Pass sales across Xbox Live Arcade, PSN and the PC, reports Joystiq, making it TellTale's fastest-selling game to date.
To celebrate the achievement, TellTale has released a trailer highlighting some of the awards and accolades the game has received since its launch.
The video game spinoff of the popular comic book and TV series features a brand new character named Lee Everett, a convicted murderer with a chance of redemption in the aftermath of the zombie outbreak.
Players will meet familiar characters such as Glenn, as well as new ones who can live or die in a branching story based on the choices made in each episode.
The Walking Dead Episode One: A New Day launched for PSN, XBLA, PC and Mac last month. An iOS port, meanwhile, is scheduled for the summer.
Episode two, titled Starved For Help, will be released as a digital download in June. It will be followed by three more episodes over the coming months.
> Read our review of The Walking Dead: Episode 1 - 'A fan-pleasing opener'
Screenshots - The Walking Dead: Episode 1 'A New Day':