Haines was educated at Latymer Upper School on a state funded scholarship, and at King's College London (MBBS) where he qualified in Medicine in 1969 with honours in pathology, surgery and pharmacology and therapeutics.

After a number of hospital appointments he trained in general (family) practice with Dr Julian Tudor Hart in Glyncorrwg, Wales.

[1][2] At various times in his career he worked in Jamaica, Nepal, USA, Canada and on sabbatical at the World Health Organization (WHO) in Geneva.

Haines was also responsible for setting up the London International Development Centre and for raising £3.7m from Higher Education Funding Council for England for this purpose.

He was chair of a WHO Task Force on Health Systems Research in 2004[10] and a member of the Council of International Physicians for the Prevention of Nuclear War at the time of the award of the Nobel Peace Prize in 1985.

[13][14][15] He also chaired an international task force on climate change mitigation and public health which published a series of articles in the Lancet in 2009.

[23] He co-chaired (with Prof. Joanna Haigh) the Academy of Medical Sciences/ Royal Society working group on 'A healthy future - tackling climate change mitigation and human health together' that reported in 2021.

[24] He currently co-chairs the InterAcademy Partnership (over 140 member science academies worldwide) working group on climate change and health.

Member of the National Academy of Medicine of Mexico; Hon Life Direct Member World Organisation of Family Doctors (WONCA); Fellow of the Royal Society of Biology; Springer Nature Visiting Professorship, Indian Academy of Sciences 2019; Fellow of the Royal Society for Public Health (RSPH); Hon.