Though a mainstay of Dublin’s defence, and a leader on the team that seeks another All-Ireland title at Mayo’s expense this Sunday, the Ballymun man’s reach stretches far beyond Croke Park to a growing portfolio of business interests and other projects and charities close to his heart.
But to the football first.
This is how most of us have come to know him after all. Few doubt his talents at both ends of the pitch but a propensity for niggle has earned him more than his fair share of what little disapproval there is to direct towards a Dublin team that speaks so softly and plays so assuredly.
McMahon earned his first All Star for his efforts last year. The man himself waves that away, like so many before him, as an irrelevance in a team game but his dismissive attitude to personal accolades becomes even starker when talk turns to Footballer of the Year.
Four of his teammates have claimed that honour in the last six seasons. Jack McCaffrey was last season’s recipient and, while McMahon had his cheerleaders, he knows a spiky demeanour on the field will always tell against him when it comes to fellow players casting their ballots.
“That’s what it is, isn’t it? It is a popularity contest. Sure I won’t be the most popular county footballer throughout my career. I accept that, once I can do my bit for the team …
“I like to think I’m a nice person off the pitch. On the pitch, I’m there to do what I can to help my team.”
McMahon has spoken honestly and intelligently about the social issues in his home of Ballymun, as well as the drug addiction that haunted his late brother’s life, and he continues to engage with authorities and volunteer groups in an effort to counter the insidious influence of drugs.
These are things worth chewing over. His businesses, too.
McMahon manages a trio of BKFitness gyms and his fascination with health and nutrition has spawned FitFood, a health food delivery company.
All of this juggled with an inter-county career that sucks time, energy and — in some cases — money from the lives of many who partake. So, how does he do it?
“I’m very lucky. The big thing in business is that if you have staff that you have to constantly manage you’re fighting a losing battle all the time. I’m lucky that I have self-motivated people in my business.
“They understand when I’m in the business end in football and take a lot of pressure off me.
“It’s no different to learning from the experience of getting to an All-Ireland final and getting to the next one. You’re doing things better every time.”
Football doesn’t last forever and he has been looking beyond it for some time. Pressing pause on everything else was never an option and if that demands even more of his time then so be it.
His is an unusual story but it isn’t unique.
Jim Gavin’s panel is replete with players who refuse to sacrifice careers for football — the unavailable pair of Jack McCaffrey and Rory O’Carroll are emblematic of that — and it is easy to see how skills crafted in business are transferrable to sport.
Win at the weekend and this Dublin team will be the first to put titles back-to-back since 1977.
Scan back over those fabled sides from the Seventies and they boast economists, surgeons, solicitors, company MDs, international soccer stars and more besides. McMahon takes the point and ponders whether the chicken or the egg comes first.
“I always ask the question to myself: would my companies be where they are today if I hadn’t got the GAA connection with Dublin? Or would the time I spent training and playing with the team... if I put that into the businesses, where would I get?
“There’s a balance. When you look at the ’70s team, you realise that the success they had - maybe from the Dublin network or the GAA network — helped them develop their careers.
“We probably have two business owners at the minute on the Dublin team, myself and Bernard (Brogan).
“The rest are doing really well. It’s a great thing about GAA, that we develop a career during our sporting career.”
Clearly, the sky blues aren’t the limit.