Fitzpatrick is the only surname with the prefix “Fitz” which is of native Gaelic-Irish origin. Donal Gěolla Phŕdraig (d. 1087), from whom the family derived their name, was the famed warrior son of Donnchadh, King of Ossory (present day Kilkenny and adjacent areas) in the 11th century. His descendants are now found in all provinces of Ireland, Laois having the largest number. By far the most important branch of the sept was and still is, the family whose Chief was known as Lord of Upper Ossory.

At one time he was almost royal ruler over Laois and neighboring Kilkenny. Following the Anglo-Norman invasion in the late 12th century, their power was vastly diminished by the ascendancy of the Ormond Butlers and other English settlers. Although their patrimony was restricted to Upper Ossory barony, the Fitzpatricks were by no means dispossessed of all their property. They were one of the original great Irish families to submit to Henry VIII, and as a result, in 1541, Brian, the first to assume the surname Fitzpatrick in place of Mac Gěolla Phŕdraig, was created Lord Baron of Upper Ossory in the 17th century, the Fitzpatricks lost considerable territory through their staunch support of James II. Nevertheless, the head of the sept received a peerage in 1714 and 1878 records show that no less than 22,000 acres of the finest land in Ossory was owned by the family. One of the best known of the surname was Brian Fitzpatrick (1585-1652), Vicar Apostolic of Ossory, murdered by Cromwellian soldiers. He was instrumental in saving the “Book of the O’Byrne,” which he transcribed, from destruction. Apart from the Earls of Ossory, the most noteworthy in modern times was Patrick Fitzpatrick (1792-1865), trusted colleague of Daniel O’Connell.