Castlehaven was involved in the defence of Ireland during the Confederate Wars of the 1640s and in the subsequent Cromwellian invasion. During the outbreak of the Irish uprising in 1641–42, Castlehaven volunteered to help suppress the Irish rebels, but because he was a Catholic he was not trusted to take command. Shortly afterwards, he was arrested and detained at Dublin Castle. Fearing that he would meet the same fate of the Earl of Strafford, Tuchet manage to escape 27 September, with the help of a friend and fled south into the Wicklow Mountains. His intention was 'to gain a passage by Wexford into France, and from thence into England;’ but coming to Kilkenny, the headquarters of the confederate Catholics, he was persuaded to accept a command in the army, and was appointed general of horse under Sir Thomas Preston, 1st Viscount Tara. It was believed among the northern Irish that his escape was a contrivance on the part of the Earl of Ormonde 'to work an understanding' between him and his kindred in rebellion, Castlehaven being related to him through the marriage of his sister with Edmund Roe Butler.