The writer - now based in Los Angeles - explained that the high viewing figures for previous miniseries Torchwood: Children of Earth guaranteed that a fourth run would eventually be made.
"I'd already moved out here [to LA] and it'd sort of been half in development, and then once those viewing figures came in it went into proper development," he revealed.
The new episodes are being co-produced by BBC Wales, BBC Worldwide and US network Starz. Davies promised that some popular American writers are being lined up for the instalments.
He continued: "We've some great names coming along - though I can't say them yet - so it's very exciting."
The former Doctor Who showrunner also admitted that he is unsure how many episodes he will be writing himself.
"That's still [to be confirmed], to be honest. I'd love to write more, but we've got a lot of interest from other writers, and I'm happy showrunning the whole thing, so… depends how it pans out, really! Plenty of time to decide."
The fourth series of Torchwood will air on Starz in the US and on BBC One in the UK.