O’Donovan is born in County Kilkenny on July 25, 1806 and is the fourth son of Edmond O’Donovan and Eleanor Hoberlin of Rochestown. His early career is likely inspired by his uncle, Parick O’Donovan. He works for antiquarian James Hardiman researching state papers and traditional sources at the Public Records Office. He also teaches Irish to Thomas Larcom for a short period in 1828 and works for Myles John O’Reilly, a collector of Irish manuscripts.
Following the death of Edward O’Reilly in August 1830, O’Donovan is recruited to the Topographical Department of the first Ordnance Survey Ireland under George Petrie in October 1830. Apart from a brief period in 1833, he works steadily for the Survey on place-name researches until 1842, unearthing and preserving many manuscripts. After that date, O’Donovan’s work with the Survey tails off, although he is called upon from time to time to undertake place-name research on a day-to-day basis. He researches maps and manuscripts at many libraries and archives in Ireland and England, with the intent to establish the correct origin of as many of Ireland’s 63,000 townland names as possible. His letters to Larcom are regarded as an important record of the ancient lore of Ireland for those counties he documents during his years of travel throughout much of Ireland.
By 1845, O’Donovan is corresponding with the younger scholar William Reeves, and much of their correspondence to 1860 survives.
O’Donovan becomes professor of Celtic Languages at Queen’s University Belfast, and is called to the Bar in 1847. His work on linguistics is recognised in 1848 by the Royal Irish Academy, who award him their prestigious Cunningham Medal. On the recommendation of German philologist Jacob Grimm, he is elected a corresponding member of the Royal Academy of Prussia in 1856.
Never in great health, he dies shortly after midnight on December 10, 1861 at his residence in Dublin. He is buried on December 13, 1861 in Glasnevin Cemetery, where his tombstone inscription has slightly incorrect dates of both birth and death.