The new virtual world will feature a "socially interactive" player-versus-environment world with Nexon providing live ops support, such as adding new content and events.
The game will launch globally iOS and Android, alongside PC and console and will be available in 14 languages.
Neither the terms of the partnership or the launch date of the title have been revealed.
Bringing Warhammer to life
"Under the creative direction of Games Workshop, Warhammer has become one of the world’s most exciting and popular game franchises, and Nexon is the global leader in developing Virtual Worlds," said Nexon vice president of development partnerships Colin Robinson.
"We look forward to extending this legacy that will bring the creative excellence of Warhammer to a virtual world for PC, consoles and mobile platforms.”
Games Workshop head of global licensing Jon Gillard added: "As one of the world’s largest game publishers, Nexon is the ideal long-term strategic partner to bring Warhammer Age of Sigmar to life in a unique new way that will appeal to gamers the world over."
"Nexon’s world-class live operations and infrastructure offers exciting opportunities for engaging current and new Warhammer fans in this massive universe. We’re really excited to see the fruits of this collaboration over the coming years."
Earlier this year, PG.biz spoke with Nexon about how the team adapted KartRider Rush Plus for mobile.