He was born in Dublin, the only surviving son of Rickard Deasy, justice of the Court of Appeal in Ireland, and Monica O'Connor.
Consequently, he won the Royal Geographical Society's Founder's Medal in 1900 for surveying nearly 40,000 square miles (100,000 km2) of the Himalayas.
In 1898 during his time in Chinese Turkestan, he collected the holotype of the jerboa species Dipus deasyi, which is named after him.
[3] In 1903 he helped promote the Rochet-Schneider Company by driving a car from London to Moscow non-stop.
In 1913, as a member of the council of the Roads Improvement Association, he formulated a scheme for a standard type of direction post and plate for adoption by highway authorities.