William Hellier Baily was born on July 7, 1819, in Bristol, Gloucestershire, England.

He was an English paleontologist. From 1837 to 1844 he was Assistant Curator in the Bristol Museum, a post he relinquished to join the staff of the British Geological Survey in London. In 1854, he became an assistant naturalist. In 1857, he was transferred to the Irish branch of the Geological Survey, as an acting paleontologist and senior geologist, and retained this post until the end of his life. He was responsible for the identification and curation of thousands of fossil specimens found in Ireland. He was the author of many papers on paleontological subjects, and of notes on fossils in the explanatory memoirs of the Geological Survey of Ireland. He published a useful work entitled “Figures of Characteristic British Fossils, with Descriptive Remarks” (1867–1875). He was also an accomplished artist and lithographer.

He died on August 6, 1888, in Dublin, Ireland.