At that point, McMahon was completing the introduction of integrated ticketing on the bus fleet, a project that was a deciding factor in his abandoning the technology sector for NZ Bus five years ago.
Previously, McMahon ran consumer electronics business Fusion and was marketing and business development manager for Navman.
Having reported directly to several boards, McMahon indicated to NZ Bus that he'd be keen to be involved at governance level.
He got his first taste of directorship three years ago when he was elected to the board of the central city business association, Heart of the City.
"We were having a bit of interaction with Heart of the City and I didn't really believe public transport was getting a fair hearing ... so rather than be the guy outside the tent I applied through their AGM as a member and got voted on."
On paper, the two bodies couldn't be more different. NZ Bus, owned by Infratil, New Zealand's largest publicly listed infrastructure investor, has a commercial, seven-member board with a focus on long-term shareholder value; Heart of the City is a not-for-profit, business advisory group with a diverse 11-member board.
"They're completely different people and they're completely different mandates, but the thing that has been interesting is, I went and did the [Institute of Directors] residential course at the end of last year and when I sat down and thought about it, the things that are challenging at NZ Bus are equally challenging at Heart of the City.
"I'm new in this director thing and my focus is still my executive career, but what I find is, it's really easy to get tied up with the here and now when you're sitting on a board.
"What's happening right now, what happened last month as opposed to where do we want this organisation to be in five, 10 years, and I think it is equally challenging on both boards."
McMahon is interested in acquiring the skills and discipline to be a director who can keep a sharp eye on the organisation's long-term goals.
"Every business has got pressure and those pressures are typically what management wants to talk about and they're typically the tactical as opposed to the strategic things." There is also a subtle tension with his role on the NZ Bus board, in that he is also an executive in the business, and he admits he's "wearing the exec hat" more often than the governance one on that particular board.
He says the Heart of the City directorship provides a nice counterbalance, where he can see the positions executives take on issues from the perspective of a non-executive director.
McMahon's potential as a board leader has been recognised by the Institute of Directors Auckland branch with an Emerging Director Award. He will be mentored by an experienced director next year, and get continuing professional development support from the institute.
He says the mentoring opportunity enables him to build on his experience of working with some of New Zealand's top directors, including Peter Maire and Andrew Clements, over the past 15 years.
McMahon says the directors he's admired are able to have a robust discussion on an issue without letting it get personal and are decisive when it's time to make a decision.
In his experience, the worst thing you can do when facing an issue is to put off making a decision.
"Sometimes it doesn't matter what you decide, it's just important that you do something; take some action." McMahon says that below the board are a lot of people wanting direction, and in the absence of a decision on a difficult issue they will make up their own minds on what should be happening - "and that can be really damaging".
Even though he's now got a governance role, McMahon is also firmly focused on the day-to-day business, which means keeping an eye on everything from bus punctuality and customer complaint levels to wage bargaining and council tenders for bus services.
Looking further ahead, he'd like to pull all the strands of his experience together to steer a business making a long-term impact on the world stage.
"There's a lot of businesses, they make it for a year, or they make it for three.
"I think the knack is, how do you make a business that endures?"
