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."
On 28 April 2009, the BBC reported that the murder of a 17-year-old student from Norfolk was a re-enactment of a scene written by Moran from the film Severance.
Moran had two features released in 2012: a horror-comedy called Cockneys vs. Zombies, which was shot in March and April 2011 and promised to be "every bit as ridiculous as its title suggests", and a thriller called Tower Block, which was shot in July and August 2011. Tower Block was the closing film at 2012's FrightFest film festival.
Moran also did an uncredited rewrite on 2014 horror movie The Borderlands, later released in the US as Final Prayer.
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 series 3 of the ITV series Primeval, the BBC One series Spooks, its BBC Three spin-off Spooks: Code 9, the NBC series Crusoe, series 3 of CBBC show The Sparticle Mystery, series 3 of Crossing Lines, and series 2 and series 3 of CBBC show Eve.
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 continued blogging from April 2010, with comments switched off. He can still be found on Twitter.
In 2008, Moran wrote a comic which featured on the Doctor Who website. His first published short story, Breadcrumbs, appeared in the Doctor Who anthology Short Trips: Transmissions. His other stories were Companion in the anthology Short Trips: Christmas Around the World, Grand Theft Planet in The Doctor Who Storybook 2009, The Haldenmor Fugue in The Doctor Who Storybook 2010, Virus in Torchwood: Consequences, Stakes On A Plane in Torchwood Magazine, October 2009, and Unplugged in Torchwood Magazine, December 2010.
His first audio work was a Highlander play, The Promise, the fourth and final story in the second season of the Big Finish audios.
He has written, and made his directorial debut with, the crime thriller web series Girl Number 9, starring Tracy Ann Oberman, Joe Absolom and Gareth David-Lloyd.
In 2013 he wrote and directed a short film, Crazy For You, a romantic comedy about a serial killer, which starred Arthur Darvill and Hannah Tointon. It premiered at London's FrightFest, and has played at the London Short Film Festival, the Seattle International Film Festival, among others. In 2015, Crazy For You won the Best Horror/Sci-Fi award at the Crystal Palace International Film Festival.
In 2014 he wrote and directed another short, Three Minutes, starring Daniel Brocklebank, which was also repurposed into a music video for the band Eighteen Nightmares at the Lux. In 2015, his short film Ghosting premiered at London's FrightFest. In 2016, he co-produced and edited Connie, written and directed by Cat Davies.
Not Guilty Pleasures, his podcast celebrating popular culture with a different guest every episode, launched in 2016.
In September 2016, Moran's new webseries Mina Murray's Journal, a modern vlog adaptation of Bram Stoker's novel Dracula, will launch on YouTube.
Moran is an atheist, and his partner is Cat Davies, a writer-director. In 2016 they formed a production company with a slate of shorts, features, and webseries.