The BBC/RTE venture has just been commissioned for a second series after it pulled in staggering audiences of more than two million viewers across the water.
In Ireland, the viewing figures are just as impressive -- nearly 900,000 for each outing. We got the low-down from his right-hand man Rory Cowan, who plays the part of Mrs Brown's gay son in the hit TV show.
And he explained why the Dublin comedian is having the last laugh when it comes to defying his critics. But how does a man who originally started off as a marketing executive with EMI, and with no professional training, get to nab a key role in one of Ireland's most successful stage productions?
As so often happens, it was sheer chance that he moved on from a role as O'Carroll's publicist to sharing a stage with the leading man in the role of his camp gay son.
"We were on a book tour in America. We were having breakfast on the Saturday, ahead of us opening in Liverpool on Monday night.
"He said to me, 'Michael (who then played Rory) is leaving to become a train driver', you're going to fill in for him. I honestly thought that was a joke, that he was messing. Then when I found out he was serious, I was like 'I can't'.
"He said, 'you have to do it. I can't get anybody else in -- you've seen the show loads of times, you'll be grand'.
"He then changed the part at the last minute and said 'I want you to jump around the stage like you're a monkey'. I stepped out on the stage in front of 1,600 people and I was nearly sick on the first night. But I had the best time and now I absolutely love it." He didn't arrive on the stage totally unprepared though, and having worked with multiple rock bands over the years, he decided he "had to go on a show" to mask his inexperience.
"I dyed my hair blonde and got all these really bright shirts. Everyone else wears normal clothes but I said 'I'm not an actor, I have to disguise this'.
"For the last season, I went in to the women's department in Top Shop and got these gold glittery trousers and a Mohican just to jazz up my wardrobe."
And even though he has been touring with the production for the past six or seven years, he admits its TV success has bowled everyone over.
"We have been absolutely stunned by the reaction to it," he explained. "The pilot that we filmed originally had 430,000 viewers and we thought, 'if it stays on that level it would be great'.
"The next week it got 700,000 and then it went up to 890,000 in Ireland. It was like that for the past four episodes, pulling in 200,000 viewers more than the Late Late Show.
"We weren't that surprised though, because it has been touring and breaking records for years. Dublin matriarch Agnes Brown was a character originally created for 2fm nearly 20 years ago, but went on to become a play, a movie starring Angelica Huston and now a hit TV series. Yet he's the first to acknowledge that O'Carroll's populist brand of humour is not to everyone's taste, even though the popularity of comedy has soared as a result of the recession.
"The critics in Ireland hate us," he continued. "Every review starts off with the phase 'foul- mouthed comedian'. They never say how the shows were all sold out and the audience are screaming with the laughter.
"But we're all earning a great living, I haven't missed a single payment on my mortgage.
"You can't please everybody. My mother hates bad language but she loves Mrs Brown. She came back from the show and said 'Oh Rory, that was one of the funniest things I've seen in my life'.
"It's just the way it works out. It was different when Brendan started out in the early 1990s to have the 'F-word' said on stage.
"But when you see what other comedians are doing now, Brendan would be considered middle of the road. I was looking at the Savage Eye and he says things like 'will we put the gays in the mincer now?'
"That could be taken up as far more dangerous than anything Brendan could say."
He is also clearly indebted to Brendan for helping him through a particularly tough time in his life.
He suffered a brain haemorrhage and a resulting stroke some 17 years ago while in his early 30s and said Brendan "made a job for me" so he wouldn't be at home thinking about his ordeal.
"It wasn't the worst thing to happen to me, I'm having the best time of my life now. I'm touring all over the place and I do get recognised quite a lot because I'm 52 and my hair is bleached blonde, who else is going to do that at my age?"
He also revealed how O'Carroll will be heading to Florida shortly to begin work on the second series of the production, which is expected to air next autumn.
"He has to go to Florida to write. His house is just too busy, there's always people coming and going. He does not get a chance to write so he goes away and spends his time relaxing and writing.
"He'll send me texts going 'you'll never believe what Rory's going to do next'. And I'm like 'What? Tell me now!'"