 He took part in the Bohemian campaign in the Thirty Years War and fought at the head of his company in the Verdugo regiment in the Battle of White Mountain, 1620.He returned to the Netherlands in 1624 and spent some time in the garrison of Ostend, with the Franciscan priest Brian Mac Giolla Coinnigh as chaplain to his company He is believed to have spent his final years in penury in the Irish College of St Anthony in Leuven, where he died about 1632.Some years later, Mac Domhnail's son, Séamas mac Somhairle Mac Donmhnaill, served as lieutenant to his kinsman, Alastair mac Colla Chiotaigh Mac Domhnaill (Alasdair Mac Colla), in Scotland (1644-45), and in Ireland afterwards, before serving in the Spanish army in the Netherlands.