William Heathcote Gilfillan, surveyor, was the son of the surveyor John Murray Gilfillan and his wife Georgina Louise Heathcote. He matriculated through the University of the Cape of Good Hope in 1881 and passed the university's examination for the Certificate of Proficiency in the Theory of Land Surveying in 1882. He was admitted to practice as a land surveyor in the Cape Colony in 1886. From 1895 to 1899 he was employed in the surveyor-general's office in the South African Republic (Transvaal). He became a naturalised citizen of the republic in January 1896, and that same year was appointed as a government surveyor. During the Anglo-Boer War (1899-1902), after Pretoria had fallen to the British in June 1900, he was put in charge of map compiling in the Field Intelligence Mapping Section of the armed forces. Towards the end of the war, in March 1902, he was appointed assistant surveyor-general of the Transvaal Colony in Pretoria. That same year he became acting surveyor-general until March 1903, when Lieutenant-Colonel H.M. Jackson* was appointed surveyor-general. Gilfillan then reverted to assistant surveyor-general, but succeeded Jackson in May 1905. In his capacity as surveyor-general he continued the compilation of the Transvaal degree sheets (scale c. 1:149 000; 1902-1909) that had been started by Jackson. He retired from his post in 1912.
Gilfillan served on the management committee of the Transvaal Museum and Zoological Gardens from 1902 to at least 1907, and in 1906/7 donated three "Bushman stone implements" to the museum. By 1903 he was a member of the South African Association for the Advancement of Science. He resided in Sunnyside, Pretoria, in 1919. He was married to Ida Isabella Southey, with whom he had three daughters.