The family had their property confiscated under the
Cromwellian regime, but it was restored to them at the
Restoration of Charles II. Justin seems to have grown up mainly in France. He became a professional soldier and showed great skill in his profession, but poor eyesight hampered his career. He entered the
French army in 1671, and then transferred to the
Duke of Monmouth's regiment, then in French pay, and served against the Dutch. On 4 March 1665, the
Second Anglo-Dutch War broke out. Three months into the war, on 3 June 1665
O.S., his brother Charles, Lord Muskerry, was killed on the flagship, the
Royal Charles, in the
Battle of Lowestoft, the first major naval engagement of the war and an English victory. His brother had an infant son, also named Charles, who succeeded him as heir apparent and was, therefore, styled Viscount of Muskerry. However, their father, the 1st Earl, died two months later, on 4 August 1665, and the younger Charles succeeded as the 2nd Earl of Clancarty. The 2nd Earl died about a year later, on 22 September 1666, still an infant. Thereupon Callaghan, the infant's uncle, succeeded as the 3rd Earl of Clancarty. Justin McCarthy came to England in 1678 and was befriended by the future James II, who generally chose soldiers, especially Irish soldiers, as his boon companions.
Charles II decided to use his services in Ireland, and made him a colonel in Sir
Thomas Dongan's regiment. On the outbreak of the
Popish Plot, however, the discovery of Colonel McCarthy's presence at
Whitehall caused uproar: he fled the country, and the
Secretary of State, Sir
Joseph Williamson, who had issued his commission, was sent to the
Tower of London. == Meddling in nephew's marriage ==