Donal III joined the so-called Irish Rebellion of 1641 under Donough MacCarthy, Viscount Muskerry, with the result that his lands were later wasted and two of his castles blown up by the Cromwellians. Later in the Irish Confederate Wars he would assist his near neighbour, James Tuchet, 3rd Earl of Castlehaven in the taking of a number of fortifications in County Cork. For all this he was eventually stripped of his estates by Oliver Cromwell in 1652. Donal married Gylles O'Shaughnessy, daughter of Sir Roger Gilla Dubh Ó Seachnasaigh, and his heir by her was Donal IV O'Donovan.