Byron won victories at Powick Bridge and Roundaway Down. He also fought at Edgehill (1642) and Newbury (1643). In December 1643 Byron was appointed Field Marshall General in North Wales. During the war Byron developed a reputation for impetuous cavalry attacks and was blamed for the Royalist defeat at Marston Moor in 1644.
In 1646 Byron went into exile and joined the royal court in Paris. Later he was appointed governor of the household of James, Duke of York. John Byron, 1st Baron Byron, died in 1652.