Mahé was raised in Tauranga and attended Tauranga Boys' College before moving to Auckland for his sixth form and university studies. He took up rowing at university and enjoyed a highly successful 20-year career in the sport. He is a two-time Olympic Champion in the single scull, winning gold in 2012 and 2016 and a five-time World Champion.

In the 2008 Olympics, Mahé had the honour of being the Flag Bearer and Team Captain for New Zealand. He was named the Supreme Halberg Award Winner in 2006 and received the Sportsman of the Year award at the Halberg Awards in 2006, 2007, 2009, 2012, and 2016. He was also inducted as a Member of the New Zealand Order of Merit (M.N.Z.M) in 2009.

After retiring from rowing, Mahé became a Financial Advisor at Forsyth Barr Limited. He holds a Bachelor of Commerce in accounting and commercial law, a Graduate Diploma of Commerce in information technology, and is an ACA with Chartered Accountants Australia & New Zealand (CAANZ). Currently he is the Mayor of Tauranga.

He is married to Juliette and has three children.