Back when he was working in the bar business (he ran a pub at the time) and struggling to make ends meet, he saw a fortune teller in London for what proved to be a life-altering experience.
"I was a complete sceptic but, once we started talking, she told me a few things that made my ears pin back," says O'Carroll.
"The first thing she wanted to do was to read my aura. So she outlined my body and said, 'Wow, you've only got one colour in your aura.' When I asked whether that was unusual, she replied, 'Yeah, you've just a golden aura and I've never seen that before.'
"She then closed her eyes, looked up and said, 'There's a line of people behind you who are dropping golden keys in your lap. I don't know what you have coming to you but, God, you really deserve it. They're all saying you deserve it.'"
O'Carroll remained unconvinced but allowed her to continue. "She then talked a little bit about my family and then two things happened: the first one was her saying, 'I see a studio, I see a stage and a microphone and amazing success'."
When O'Carroll suggested she had envisaged his attempts to promote a band, which was part of the reason he was in London, she insisted it was him she had seen at the microphone. "And she added, 'Do something for me - remember this: Glasgow. It'll change your life.' I was like, 'Sure, okay...' But I forgot (about) it almost as soon as she said it."
It was not until later that night that O'Carroll was forced into a re-think because, at the same session, he had agreed - albeit reluctantly - to write down a message from beyond the grave relating to someone called Chalky, which read, "Of course I'm proud of you, I've always been proud of you, and I love you."
And it was while relaying the story and the message over a meal with a business acquaintance and friend that evening that he was stunned to discover it had been intended for his dinner companion. What's more, it had come from his friend's late father, who had been told by his son at the moment of his death: "Don't you dare die without telling me you're proud of me and don't you dare die without telling me you love me."
Adds O'Carroll: "The very first success we had with the play (of Mrs Brown's Boys) was in Glasgow, at the Pavilion Theatre; and when Stephen McCrum, (executive producer of comedy) from the BBC saw the play, it was at the Pavilion; and when we made the TV series, it was at the BBC in Glasgow. So it's been Glasgow and it has changed my life."
O'Carroll now lives in Florida with his second wife, Jennifer Gibney, and rightly savours the success of the Bafta-winning show, which beat Downton Abbey and Call The Midwife to the top of the Christmas viewing figures last year (with 9.4 million), and sold more DVDs in 2013 than anything else on film or television in the UK other than James Bond's Skyfall.
But how did he keep the faith, I ask, especially as he had to wait until he was well into his forties to achieve it, taking various jobs as a waiter, milkman, pirate radio DJ and painter-decorator in between trying to gain a foothold as a comedian?
"I really don't know what kept me going," says the 58-year-old, with a laugh. "I used to drive 180 miles to a gig, there were 14 people there, you had already spent £60 in petrol, you are also on the door, it's £2 in, so it's £28, you go on, you do the gig, you come off the gig and have to make your way home, and the money you've collected on the door is barely enough for the petrol to get back. And yet the next morning you get up and you do the next gig and go, 'What in the hell made me think that this would work?'
"But I think it was probably because I was put in a position that there was nothing else I could do at that time. There was no work available. It was 1989-90, which was the last Irish recession, and there were no other jobs. So maybe what kept me going was the fact I had no choice but to keep going."
Another key to his success was his family and, in particular, his late mother. The youngest of 11 children, O'Carroll took it upon himself from an early age to make her laugh as often as possible and, in doing so, discovered his passion for comedy.
"My mother was 46 when I was born, but by the time I got into my formative years, all of a sudden she retired from politics (having been an Assembly Delegate for the Labour Party). Well, first of all, my dad died when I was seven, but by the time I was nine she had retired, which meant it was just me and her.
"That meant I had the undivided attention of this genius of a woman. The comedic end of things probably stemmed from that. First of all, she was a very huggy person. So, my life's goal from that age was to make my mum laugh. That's all I wanted to do - and I did many, many times. And she was a big woman, so she rocked with laughter and it made me feel so good."
It's this desire to continue making people laugh that informs everything that O'Carroll has attempted with Mrs Brown ever since, and which makes him determined not to "betray" her fans with the new movie.
"I didn't want to do the cliched thing of taking her to Spain or America or Africa, like a Crocodile Dundee kind of thing. I just wanted to expand her world and tell her story and give the audience the chance to peek into the bits that they know about (but never see). It's Mrs Brown in her own world but on a bigger scale."
O'Carroll isn't finished yet. In addition to the film, there are also regular theatre tours of the show as well as an animated version, the pilot for which is already complete. O'Carroll has even talked of further movies, possibly even a trilogy.
That he remains so tireless is, once again, down to his mother and another pearl of wisdom that she imparted: "My mum had a great outlook on success, and that is if something is successful, you've got to treat it like disco music - don't analyse it, just dance with it. And since those first five minutes on the radio, I've just been dancing."
And on that note, he waltzes off, out of the room.
Mrs Brown's Boys D'Movie opens in cinemas tomorrow