The final use Conwy castle saw was in the English Civil War in 1642. The castle was held by the supporters of Charles I until 1646 when it was surrendered to the Parliamentary armies. In 1665 the remaining lead and iron were stripped out of the castle and it fell into disrepair.
In 1401 Rhys ap Tudur and his brother Gwilym successfully captured the castle by posing as carpenters, killing the watchmen on duty, and opening the gates. They held the castle for 3 months before negotiating a surrender with Henry IV.