Coleman entered politics in 2005 winning the seat of Northcote for National and spent over twelve years in parliament, serving as Minister for Sport and Recreation from 2014-2017, as well as holding the positions of Minister of Health and Minister of Defence. As Minister for Sport he had extensive involvement with the New Zealand Olympic Committee and attended the Vancouver 2010 Winter Olympics and Rio 2016 Olympics as the New Zealand Government's Representative.

Following his departure from Parliament, Coleman became Chief Executive and later a Board Director of Acurity Health Group. He is currently a Board Director and Chair of the Clinical Committee for Metlifecare Ltd, a retirement village operator, and also serves as a director of Habit Health Ltd. Additionally, he remains a registered medical practitioner.