Wheler served as a major in a Royalist Horse (cavalry) regiment from very early in the Civil War until 1644 when, he transferred to a regiment of foot in which he served until early in 1646 when he surrendered to Parliament and was allowed to go into exile. In 1656 he was commissioned in to King Charles II's Guards—then a regiment in the Spanish army—as a captain, his regiment fought under Tunney at the Battle of the Dunes (1658).