First Earl of Tryconnel and last Chieftain of the O'Donnell's. Born in 1575 he was one of nine children. The younger brother of the famous Red Hugh O'Donnell he became Chieftain of Tyrconnel after his brothers death in Spain in 1602.
Rory took part in many of the battles of the Nine Years War and was at the Battle of Kinsale. He was awarded a pardon from King James I for his part in the rebellion and was knighted as Earl of Tyrconnel. He married, Brigit Fitzgerald, the daughter of the Earl of Kildare shortly after, to whom he had three children.
Rory left with his fellow Earls in 1607. In his haste he left his pregnant wife behind who had been visiting relatives in Kildare. He was given refuge in Rome but died in 1608. He is buried alongside O'Neill at the alter of the Franciscan Church of St Peter in Montario in Rome.