During the English Civil War, Wentworth was the Sergeant-Major-General of Horse and commanded the Prince of Wales's Regiment of Horse. He saw action at Tipton Green, Cropredy Bridge, and possibly at Newbury, all in 1644; at Langport in 1645; and at Worcester, the final battle of the English Civil War in 1651. He fought most battles alongside his father. When the Royalists were defeated, Lord Wentworth accompanied the court into exile. He raised a regiment (which later became the Grenadier Guards) at Bruges as a bodyguard to the exiled Charles II.