King was born in Cork, the eldest son of Sarah King (her married and maiden name) and Joseph King (grocer and naval supplier).[3] He attended Trinity College Dublin where he was elected a Scholar in 1835.[4] He was a Senior Moderator (with Gold Medal) BA in mathematics 1838, also winning prizes in Hebrew and Divinity.[4][3] He held various positions for the first 20 years of his career, including serving as a curate in counties Dublin, Londonderry and Armagh. From 1858 until his death he was headmaster of the diocesan school in Ballymena, County Antrim.[3][1]
His numerous publications include A Primer of the History of the Holy Catholic Church in Ireland (3 volumes, 1849-1855) and a memoir on the early history of the primacy of Armagh (1854). He was also an Irish language scholar, and authored several books in Irish, including a grammar and a reedited version of the Book of Common Prayer in Irish (1860).[3][1][2]
In 1857 he married Harriette Stuart (daughter of Alexander Stuart, rector of Killincoole, Armagh). The couple had nine sons, of whom Richard King became dean of Derry.[3]