Born in York, Moran's first produced work came as the result of a competition run by the Sci Fi Channel. The competition asked for writers to submit short science-fiction themed film scripts. Moran won, and his entry Cheap Rate Gravity was produced and shown both on the sci-fi channel and in front of full length movies, including Final Destination 2.

Moran secured an agent at the PFD Literary Agency from the strength of the competition win, a spec film script, and a six-part TV drama entitled The School. He wrote the entire run of The School on spec, later saying he was unaware that generally only a pilot is written until a production company shows interest. Moran claims the series is still his favourite of his own works.

Moran scripted the 2005 film Severance, which concerns office workers on a team building trip being stalked by a masked killer. Talking about where the idea for Severance came from, Moran said "I'd been trying to think of a good horror idea, and one day had a really bad commute home — yuppies in pinstripe suits were everywhere, pushing past me, jumping the queue, and generally being the ignorant scumbags that they are. So, in a flash of temper, I decided to kill off some yuppies in a horror — take them to a cabin, and pick them off one by one. Once I'd calmed down, I thought that was a pretty good idea — take some standard, British office types, and throw them into a cabin-in-the-woods horror, see how they react. And it developed from there."

Moran is currently working on another feature length horror script, Curfew, for the same company that produced Severance.

Moran's television writing debut was writing episodes for Doctor Who, and its adult themed spin-off, Torchwood. He lobbied his agent for many years to get him a job on either show.

Moran's first Torchwood episode, "Sleeper", was the second to be transmitted in the second series, and concerns a burglary that goes wrong, revealing a plot that leaves the whole planet in danger. There are many allusions to terrorism during the episode, and filming on several controlled explosions in Cardiff was almost disrupted by a real terrorist attack in Glasgow. "Sleeper" was broadcast by BBC Two on 23 January 2008. Moran also co-wrote the Torchwood episode, "Day Three" of "Children of Earth" with Russell T Davies which was first broadcast on 8 July 2009.

Moran's Doctor Who episode, "The Fires of Pompeii" — set during the eruption of Mount Vesuvius — was broadcast on 12 April 2008 as part of the revived programme's 4th series.Moran also wrote episodes for the ITV series Primeval, the BBC One series Spooks, its BBC Three spin-off Code 9, and the NBC series Crusoe.

James Moran has a personal blog called The Pen Is Mightier Than The Spork. Moran started writing it around the same time as he started writing the screenplay for Severance, documenting the entire process all the way to the DVD release, and up until July 2009 he still regularly updated about his current projects. He also endeavoured to answer any reader's questions and offer advice to other would-be screenwriters. He can still be found on Twitter. Moran is an atheist.

In 2008, he wrote a comic which featured on the Doctor Who website. His first published short story, Breadcrumbs, appeared in the Doctor Who anthology Transmissions.

He has also written, and made his directorial debut on the Internet crime thriller Girl Number 9, starring Tracy Ann Oberman and Gareth David Lloyd.

Moran has recently moved from PFD to The Agency.