In July 1810, Hay was sent back to the Peninsula with the 3rd battalion, 1st Foot of which he again obtained command on 4 August. Hay fought at the Battle of Bussaco on 27 September, where Wellington's army drove off a superior French force under Marshal André Masséna. Promoted to major-general on 4 June 1811, Hay went on to fight in the important victories at the Salamanca on 22 July 1812 and Vitoria on 21 June 1813, in which his son, Captain George Hay received a mortal wound.