After his acquittal, Muskerry was again allowed to embark to Spain but went to France where his wife lived with her sister Mary Butler, Lady Hamilton, in the convent of the Feuillantines in Paris. His daughter Helen was harboured at the abbey of Port-Royal-des-Champs, near Versailles, together with her cousin Elizabeth Hamilton. The abbess, La Mère Angélique, trying to help the Irish and to raise funds for Charles II, wrote to Queen Marie Louise Gonzaga of Poland in 1654 proposing to employ Muskerry and his 5,000 Irish in Polish service. In 1655 Muskerry and Bellings then led these 5,000 to Poland. This was the year of the Deluge, the Swedish invasion of Poland that started the Second Northern War. Muskerry and Bellings returned with £20,000 for the King. In 1657 the King sent Muskerry and Sir George Hamilton to Madrid to ask the Spanish to send their Irish exiles to Ireland. Muskerry's eldest son fought with his regiment at the Battle of the Dunes on 14 June 1658 where it formed part of the English royalist army under the Duke of York that fought together with the Spanish on the losing side against the victorious French and Protectorate English. The King, in exile at Brussels in 1658, rewarded Muskerry with the title of Earl of Clancarty. By this advancement, the title of Viscount of Muskerry became the highest subsidiary title of the family, which became the courtesy title of his eldest son and heir apparent.