Upon William of Orange's invasion of England, Barrymore came out for William against James II and was subsequently appointed lieutenant-colonel in William's army on 31 December 1688. After the outbreak of the War of the Spanish Succession in 1702 he purchased for 1,400 guineas the 13th Regiment of Foot from Sir John Jacob, 3rd Baronet (his brother-in-law) and became Colonel of the Regiment. He was in turn appointed brigadier-general (c. 1707), major-general (1709) and lieutenant-general (1711). He served under Lord Galway and was captured after the Battle of Almansa in 1707. Upon the accession of the first Hanoverian monarch George I and his proscription of the Tories in 1715, Barrymore was forced to sell his regiment.