Sinton joined the Indian Medical Service in 1911, coming first in the entrance examinations, but before being posted to India was seconded as the Queen's University research scholar to the Liverpool School of Tropical Medicine where his contact with Sir Ronald Ross may have influenced his later career as a malariologist.

On 21 January 1916 at the Orah Ruins, Mesopotamia, Captain Sinton attended to the wounded under very heavy fire and the citation to his VC reads: For most conspicuous bravery and devotion to duty.

Although shot through both arms and through the side, he refused to go to hospital, and remained as long as daylight lasted, attending to his duties under very heavy fire.

He became Manson fellow at the London School of Hygiene and Tropical Medicine and at the malaria laboratory of the Ministry of Health at Horton Hospital, near Epsom.

He then worked as consultant malariologist to the War Office, travelling widely to Assam, Australia, Burma, Ceylon, India, New Guinea, and the Solomon Islands, where his expertise in malaria was invaluable.

His name is remembered in Sinton Halls, a student housing block at the Queen's University, Belfast, where he sat on the senate and was a Pro-Chancellor.