He is best remembered for his discoveries of Leishmania donovani as the causative agent of visceral leishmaniasis, and Klebsiella granulomatis as that of donovanosis.

He participated in British expeditions to Mandalay in Burma, Royapuram and Mangalore in India, Afghanistan, and finally Madras (now Chennai), where he spent the rest of his service.

In 1879, when he was thirteen years of age, he was sent to Cork to live with his paternal grandfather, the Reverend Charles Donovan, a Church of Ireland rector.

He continued his education and entered Queen's College, Cork, enrolling on the arts programme, which would have included subjects relevant to the study of medicine.

[2][4] After clinical training in Dublin hospitals for two years, Donovan was commissioned as captain in the Indian Medical Service in 1891.

After seven years of service in several expeditionary forces in Burma, India and Afghanistan, he was finally posted in Madras in 1898.

On 17 June 1903 Donovan found the parasites (by then known as "Leishman bodies") from the spleen tissue and in the blood of an infected young boy who was admitted to the Government General Hospital.

Donovan sent some of his slides to Ronald Ross, who was in Liverpool, and to Alphonse Laveran at the Pasteur Institute in Paris.

Laveran and his colleague Félix Mesnil identified the protozoan (and yet wrongly) to be members of Piroplasmida, and gave the scientific name Piroplasma donovanii.

It was Ross who resolved the conflict of priority in the discovery and correctly identified the species as member of the novel genus Leishmania.

He gave the popular name "Leishman-Donovan bodies", and subsequently the valid binomial Leishmania donovani, thereby equally crediting the two rivals.

In 1905 Charles Donovan prepared tissue smears from the ulcerative mouth of a ward boy in Madras hospital.

The description was similar to Donovan's bodies, hence, they were considered to be members of Sporozoa, and the scientific name Donovania granulomatis was introduced.

Aragão and G. Vianna gave the binomial Calymmatobacterium granulomatis noting their similarities to bacteria from their (rather dubious) cell culture.

He was a dedicated doctor and inspirational leader that even the sweepers at Madras hospital were able to prepare excellent microscopic slides.