He spent the last twenty years of his life studying the evolution and systematics of New Zealand cicadas.
[4][5] Fleming was a Coastwatcher on the Cape Expedition in the Auckland Islands from 1942–1943 during World War II.
[6][7] Fleming graduated from the University of Auckland in 1952 with a doctoral thesis on the geology of Whanganui.
In 1997, Trevor H. Worthy commemorated Charles Fleming in the species' epithet of the prehistoric rail Pleistorallus flemingi from the mid-Pleistocene of New Zealand.
[12] He was promoted to Knight Commander of the Order of the British Empire in the 1977 New Year Honours, for services to science and conservation.