Passing into the service of France after the treaty of Limerick, he could only obtain the rank of captain in the marine regiment of the Irish Brigade.
O'Donnell, whose commission was dated 4 February 1692, served with this regiment on the coast of Normandy during the projected invasion of England, which was averted by Edward Russell's victory at the naval Battle of La Hogue, and afterwards in Germany in the campaigns of 1693–1695.
[1] Transferred to the Low Countries in 1707, he fought against the Duke of Marlborough at the Battle of Oudenarde in 1708, succeeded Nicholas FitzGerald as colonel of a regiment on 7 August 1708, and commanded the regiment of O'Donnell of the brigade in the campaigns of 1709–1712, including the Battle of Malplaquet and the defence of the Lines of Arleux, of Denain, Douai, Bouchain, and Quesnoy.
[1] A jewelled casket containing a Latin psalter said to have been written by the hand of St. Columba, and known as the "Cathach of Columb-Cille", belonged to Brigadier O'Donnell, and was regarded by him, in accordance with its traditional history, as a talisman of victory if carried into battle by any of the Cinel Conaill.
[2] His son, Sir Richard Annesley, entrusted the relic to the Royal Irish Academy,[1] in whose custody it still remains.