An author of Black Library who has worked to fill the plotholes of Warhammer Fantasy and develop the Age of Sigmar setting.
He was put in charge of writing the first and fifth/final novels of The End Times (The Return of Nagash and The Lord of the End Times), doing his best to actually bring a decent narrative to what is arguably Games Workshop most controversial action.
After that he has been in charge of fleshing out the Age of Sigmar universe, which has allowed the development of the Stormcast Eternals into quite interesting characters (he brought in some female stormcast, a stormcast who may have been an elf originally and worked to bring some character to Tornus The Redeemed), he is also developing a cast of characters for his stories, allowing for AoS to have its own dramatis personae. His characters come from multiple races and backgrounds and all of them are fleshed out. Even his villains - even daemon characters - are actual characters rather than two-dimensional plot devices. In an interview, this is because there's a maxim Josh applies to each character he writes; "Everyone is the hero of their own story".
With the Advent of AoS 2.0 he wrote "Soul Wars", reintroducing Balthazar Gelt, making the new Sacrosanct Chamber more human, and pitting Death and Storm against one another in a philosophical debate. He's also the main guy behind fleshing out the personality of established Warhammer characters including big bone daddy himself. Speaking of the death faction, Josh also seems to be quite the Arkhan/Neferata shipper (continuing what was set up in the Time of Legends Nagash trilogy by Mike Lee), but it's actually well-written and true to their respective characters.
Additionally expanded the fluff for 40k, expanding characters such as Fabius Bile and Trayzn the Infinite.
Sadly, no longer with Black Library, due to them not wanting to greenlight a lot of his awesome story ideas.