Muir Gray entered the public health service by joining the City of Oxford Health Department in 1972. The first phase of his professional career focused on disease prevention, followed by the development of the NHS screening programmes as well as services aimed at bringing knowledge to patients and professionals, including the NHS Choices.  He has also been instrumental in setting up the Centre for Evidence Based Medicine and the Cochrane Collaboration in Oxford.  During this period, he was appointed as the Chief Knowledge Officer of the NHS in England.  In 2006 he joined the Department’s Commissioning Directorate and published the first Annual Population Value Review in 2006.  In 2010 he set up the NHS Rightcare programme with Phil de Silva and remains an adviser to the programme and to Public Health England on population healthcare.

He is now working with both NHS England and Public Health England to bring about a transformation of care with the aim of increasing value for both populations and individuals launching the NHS Atlases of Variation. He set up the Centre for Sustainable Healthcare and Better Value Healthcare  and has published a series of How To Handbooks for example, How 'to Get Better Value Healthcare, How To Build Healthcare Systems and How To Create the Right Healthcare Culture and, with Professor David Kerr, How to Get Better Value Cancer Care.

His hobby is ageing and how to cope with it and he has published a book for people aged seventy called Sod 70!  one for the younger decade called Sod60! And a book on activity Sod Sitting, Get Moving.