He entered the army as an ensign in the 51st (2nd Yorkshire West Riding) Regiment of Foot on 6 December 1809. In January 1811 the 5lst joined Lord Wellington's army while encamped within the lines of Torres Vedras, and Elliott's first battle was Fuentes de Oñoro. He was present at the capture of Ciudad Rodrigo and of Badajoz, and at the battle of Salamanca, and was promoted lieutenant on 13 August 1812. During the retreat from Burgos he acted as aide-de-camp to Colonel Mitchell, commanding the first brigade of the seventh division, and was wounded in conveying despatches under fire.