Originally from Adel, the Leeds Grammar graduate, 42, moved to California and has spent years hustling to get himself recognised in Hollywood.
-> All you need to know about Screen Yorkshire - the team who backed Peaky Blinders, Official Secrets and All Creatures Great and SmallNow his second feature, Headshots, has won a string of awards on the film festival circuit in the USA.
His wife Rochelle Carino, a costume designer and co-writer, persuaded him to make the film, which came out over the Atlantic last year.
It follows a young British actress who moves to Los Angeles to be a star, only to cross paths with a serial killer in her acting class - but her family come over to "sort out" the culprit.
Speaking about the film's inspiration, Mr O'Neill said: "Having spent a lot of time in LA, I had seen that it was a very nomadic place, with people coming and going all the time and suddenly they’re just not there anymore.
-> How the BBC's Gentleman Jack sparked global awe of Yorkshire rebel Anne Lister and Shibden Hall"Listening to tales of actresses going to 'auditions' or 'photography sessions' in dodgy places to meet with complete strangers who might not even have a film to actually cast sounded terrifying. But it’s real and it happens every day.
"And the statistics of the amount of people who go missing in LA county is enough to fill Elland Road football stadium."
Mr O'Neill believes it is the type of film the "master of suspense" Alfred Hitchcock might be making today if he were still alive.
He began writing feature-length screenplays while at school, wanting to create scripts akin to some of his own favourites.
-> How Victorian Bradford made its mark on the history of cinema"I was inspired by buddy cop films like Lethal Weapon and 48 Hrs, British TV comedy shows like Blackadder and horror movies like The Thing.
"The fast paced banter fascinated me as it seemed they were doing the same kind of clever back and forths in Hollywood as they were in Headingley, so it seemed rather universal."
He won a place at the National Youth Theatre, which counts Daniel Craig, Rosamund Pike and Sir Daniel Day-Lewis among its alumni.
Mr O'Neill went on to study film at the University of East Anglia in Norwich and San Francisco State University.
After graduating, he came back to Leeds and worked in various jobs including roles at banks and selling double-glazing over the phone - but never gave up on his dream and "kept firing out screenplays" to Hollywood production companies.
"Eventually, one of them asked me to go in for a meeting, so I flew over for a week and ended up staying three months," he said.
"I would call 25 companies a day trying to get a meeting and two would usually invite me to come in - which I attribute solely to a Leeds gift of the gab. And the fact Hollywood doesn’t have many fast talking Northerners knocking on doors with scripts in their hands."
He added: "The way I made contacts was I would arrange a meeting on a studio lot, fill up a backpack with screenplays and copies of short films I’d done, then walk around the lot after my scheduled meeting and literally just go in to the offices of various production companies and introduce myself.
"After lots of coffees and much rejection, I finally landed a writing deal with the producers of Wedding Crashers."
His first feature film, Absolute Debauchery, a buddy crime movie he wrote, directed and co-starred in, was also released last year.
Headshots, however, has further boosted Mr O'Neill's profile.
It is featured as an official selection at Culver City Film Festival, Olympus Film Festival, Anaheim Film Festival, Action On Film MegaFest Las Vegas, Hollywood Dreams International Film Festival and the World's Independent Film Festival in San Francisco.
The movie has also won a number of awards including Best Film, said Mr O'Neill.
He said: "It’s a really validating thing to be chosen as an official selection to play on the bill. When they turn around and give you an award on top of that, it's really encouraging and we feel very grateful and honoured that they enjoyed Headshots so much.
"To have five of them do it is mind-blowing. Of course, there are many festivals we submitted to where Headshots wasn't selected, but it's swings and roundabouts and the highs of being an award winner at five festivals very much exceeds the lows of not being selected for others."
The film is due to be released on Amazon in October in time for Halloween - and he hopes to return home to Leeds again in November.
He said: "We are hoping to bring it to the Leeds Film Festival this year - if they’ll have us.
"After all, you don't see many horror thrillers with Northerners going to LA to sort out a serial killer and what better place would there be to give the film its UK debut than the Leeds International Film Festival, my hometown. That would be amazing."