Warhammer: End Times - Vermintide, developed by Swedish studio Fatshark, has sold over 500,000 copies on PC since its release in October 2015.
"We are really happy with the sales so far. We reached half a million copies much faster than we estimated. As a small studio, this really is an amazing milestone for us. The office is a hive of excitement," said CEO Martin Wahlund.
"We are overwhelmed by the positive response from both players and critics alike, and this has given us the extra drive to continue providing exciting and engaging content so that everyone can continue to enjoy the game long into the future."
The game is also due for release on PS4 and Xbox One later this year.
Fatshark was founded in 2008 and its portfolio includes Bionic Commando Rearmed 2, War of the Vikings and Escape Dead Island.
"The only thing we said when we started was that 'we need to make a great game.' It's not to make money, which sounds silly, and it shouldn't be to get famous. If you make a great game, people will love it and everything else comes from that. The only thing we can really affect is whether or not we make a great game. It could be a bit naive, but that's what worked for us," Wahlund told GamesIndustry.biz in October 2015.