Not content with being back this year at that same venue with The Krankies in panto (he's Dick McWhittington), John has filmed a new BBC quiz show, Pressure Pad, going out in November and a song contest series with ABC in America.
And not only did he turn down the chance to star in a Hollywood movie with Drew Barrymore, the Glasgow-born all-round entertainer is also a successful businessman, with property and skin care companies.
The Scot, whose family emigrated to Illinois when he was eight years old, has homes in London, Wales and Palm Springs, and owns 10 cars.
Ergo, he has to be an insufferable egomaniac. Right?
Doesn't seem so at all. After interviewing the star several times, his head still seems contained enough to be able to wear Jimmy Krankie's school cap.
"I was asked to do a couple of big film roles", offers the musical theatre star in a Glasgow accent that re-emerges when he comes within sight of the Clydeside cranes.
"In fact, I was offered a film with Drew Barrymore, but I had already committed to panto.
"I know a lot of actors who would have thought 'To hell with panto' and gone off to Hollywood, but that's not my work ethic. And the right film will come along one day."
He's right. Many actors would have walked barefoot to Hollywood. But Barrowman has commitment and loyalty to audiences, to The Krankies and producer Michael Harrison.
And he has showbiz in perspective.
"I didn't get into this business to become a celebrity," he says in serious voice.
"I enjoy the idea of making people laugh, making them happy but I also enjoy the other businesses I run with my business partner.
"And I love tinkering with my cars, even if it's just replacing the battery."
He adds, with a circumspect air: "Entertainment is my life, but I also have a life outside of it."
John Barrowman seems to have the life/work balance just about right. But then the 46 year-old has been in the business long enough to know if you don't keep it in perspective, there's a price to pay.
He's learned along the way, from appearing in high school musicals to studying musical theatre in San Diego, going on to feature in a range of West End shows from the age of 23.
John also showed he was just as adept in front of a camera. One of the original hosts of kids' Saturday morning show Live & Kicking, he graduated to big telly with the likes of This Morning, and How Do You Solve A Problem Like Maria.
Meantime, he's made his dramatic mark in the likes of Torchwood and Desperate Housewives.
He certainly makes no apologies for acquiring the trappings of success.
"I've got 10 cars," he says, in response to the question. "But I live and work in different places so I use them all. Each garage is full.
"The flashiest car? I don't consider it to be a flashy car but I guess it's my Porsche Cayenne, or maybe or the S Class Mercedes. And I don't see them as an indulgence. I think if you work hard you should treat yourself."
He dismisses the Scots who can't applaud their own success stories.
"That's their problem. It's not mine," he says. "I learned a very big lesson early on and it's stuck with me. It's that not everybody is going to like you. And now I don't worry about what others think. And if I want to buy a Porsche I will.
"What I do when I get a Porsche is I tweet the pics to my fans and say 'Thank you very much, for without you I wouldn't have this.'
"Or the homes in London, Wales and Palm Springs."
He's on the hunt for a Scottish home, to add to his addresses around the world. And why not come back home, at least during the panto season?
"It will be a place for friends to come stay," he enthuses. "And Ian and Janette will live with me during the panto run. It will be a house of fun."
John Barrowman uses the word 'fun' a lot.
HE says: "I've had my share of ups and downs, but think if you're open and honest people will respect you.
"I go to work, do my job then go home, put my feet up and have a vodka and soda and scratch the dug's belly," he says, revealing a film star smile.
"I still go to Tesco, I still go to the cinema, and I still fly British Airways in the same cabin as everyone else. I don't want to be treated differently."
He's excited about working with his Krankie chums again, and coming back to Glasgow panto for the fourth time.
"Some said we'd never be able to work together, but The Krankies don't have an ego and neither do I."
Yet, John won't work with horses on stage again, after fears he'd broken his back last year when the horse reared and he was thrown into the air. His cousin's son Greg Barrowman came on as his understudy.
"As I was laying there on the stretcher, in a neck brace, with Janette crying her eyes out, Greg smiled and said 'I'm getting ready to go on stage, John. See you later.' And off he leapt."
The show had to go on, John.
"Yes, it's showbiz," he says, grinning. "And it's moments like that help keep you real."
l Dick McWhittington, SECC, December 14 - January 5