With the outbreak of war he joined the Chester garrison which was commanded by his son-in-law John, Lord Byron. Although his younger son was captured in a skirmish in 1645, and that it was falsely rumoured that his wife Frances had been killed, Kilmorey escaped at the end of the siege (late January) and made his way to Oxford, which was still held by a large Royalist garrison, where he surrendered when the city surrendered (24 June 1646).
With the war's outbreak, he joined the Chester garrison commanded by John, Lord Byron. Despite his younger son being captured in a skirmish in 1645 and rumors falsely stating that his wife Frances had been killed, Kilmorey escaped at the siege's conclusion (late January) and made his way to Oxford, which was still under Royalist control, where he surrendered when the city fell (24 June 1646).