Capell was one of the chief Royalist leaders in the second Civil War, but met with no success, and on 27 August 1648, together with Earl of Norwich, he surrendered to Lord Fairfax at Colchester, on the promise of quarter for life. This assurance was afterwards interpreted as not binding the civil authorities, and his fate for some time hung in the balance. He succeeded in escaping from the Tower of London, wading the moat once he had got over the walls, only to be betrayed by a Thames waterman, who had been engaged to row him from a hiding place at the Temple to one in Lambeth. He was again captured and was condemned to death by parliament, on 8 March 1649, and beheaded together with the Duke of Hamilton and the Earl of Holland.