The figure includes sales across PC, Mac, Linux, PlayStation 3, and PlayStation Vita.
Thomas Was Alone was released on PC in 2012, with the PS3 and PS Vita versions following thereafter.
Bithell recently revealed a follow-up called Volume, a top-down stealth game set to release in 2014. The game will also allow players to modify levels and share results with the community.
For more on Thomas Was Alone, check out GameSpot's review.