Davis was born in Milford on Sea, Hampshire, England, on 25 April 1947,[1] and spent his childhood in Tanzania, where his father worked for a mining company.

[3] Davis gained a master's degree in sociology and statistics at the London School of Economics.

[9] Previously he served as Professor of Public Health at the University of Otago's Christchurch School of Medicine.

Davis has achieved international recognition in his field, having worked as a consultant for the World Health Organization.

[10] In 2019 Davis became a City Vision candidate for the Auckland District Health Board and was subsequently elected.