Originally from the North-East of England, Dr Johnson qualified as a doctor in 1993 and has worked continuously as an NHS paediatrician at Hinchingbrooke Hospital since 2007.His frustration at dealing with health inequalities on a daily basis drove him to be active in local politics , including serving as a district councillor, and standing as a parliamentary candidate for Huntingdon in 2015.In May 2021 in a surprise election result ,against the then national trend , he was elected as the Labour Metro Mayor for the Combined Authority of Cambridgeshire and Peterborough where he served for 4 years before standing down in May 2025 . Advocating that the 3Cs of “compassion, cooperation to delivery for the community” had to be at the heart of all local government public policy he refocused the work of the Combined Authority to be a catalyst of beneficial change - collaborative work delivering local solutions for inclusivity, for more equal access to opportunity and resources, for ‘good green growth’, and for affordable, public transport that serves communities and respects the environment.

Dr.Johnson’s compassionate approach was nationally recognised for turning around ,improving and leading the Combined Authority to success . Trailblazing as a more “rural” Combined Authority it has been highly rated for its active travel plans, has championed local bus services in the face of cuts, been a powerful support for business during the pandemic and into the high street recovery. It has also revamped its transport and connectivity strategy to prioritise left-behind communities, address digital exclusion, and link more people to education, training, work, and leisure opportunity.

Now at a professional and political career hiatus he is back working at his local hospital and describes himself as “ The Ragged Trousered Paediatrician -resting but preparing himself for the next fight for social justice” .

Dr Johnson lives near the Cambridgeshire market town of St Neots, with his wife, who is a fellow doctor, and their three children, revelling in a “weekend life based around the participation and enjoyment of sport, dance and acting activities.