Fel Prif Swyddog Meddygol Cymru, bydd Dr Atherton yn gyfrifol am ddarparu cyngor proffesiynol annibynnol i'r Prif Weinidog, Ysgrifennydd y Cabinet dros Iechyd, Llesiant a Chwaraeon, y Gweinidog Iechyd y Cyhoedd a Gwasanaethau Cymdeithasol a’r Cabinet ynglŷn â materion yn ymwneud ag iechyd ac iechyd y cyhoedd. Bydd hefyd yn gweithio gyda  sefydliadau trwy Gymru i leihau anghydraddoldeb ym maes iechyd, ac i wella iechyd.
As Chief Medical Officer for Wales, Dr Atherton will be responsible for providing independent professional advice to the First Minister, the Cabinet Secretary for Health, Well-being and Sport, the Minister for Social Services and Public Health and the Cabinet on health and public health matters, as well as working with organisations across Wales to reduce health inequalities and improve health.