On the outbreak of the English Civil War, Northampton was entrusted with the execution of the Commission of Array in Warwickshire. After varying success and failure in the English Midlands, he fought at the Battle of Edgehill and, after Charles I of England's return to Oxford, was given, in November 1642, the military supervision of Banbury and the neighbouring country. He was attacked in Banbury by the parliamentary forces on 22 December, but relieved by Prince Rupert of the Rhine the next day.