Cathbarr married Rosa O'Doherty, the sister of the Inishowen lord Sir Cahir O'Doherty who fought on the Crown's side during Tyrone's rebellion but later launched O'Doherty's Rebellion by burning Derry. In 1607 Cathbarr and Rosa accompanied Rory in the Flight of the Earls to Continental Europe. The following year Cathbarr and Rory both died of fever in Italian exile and the leadership of the O'Donnell's passed to Rory's young son.