Promoted to colonel in 1808, Peacocke served with his regiment at the beginning of the Peninsular War, fighting at the Second Battle of Porto. In June 1809 he left regimental service to take up post as Commandant of Lisbon, which he would hold until the end of the Peninsular War. Tasked with organising troops ready to join the Duke of Wellington's army, as well as with arranging the rehabilitation of injured soldiers and coordinating with the Portuguese government, Peacocke was promoted to brigadier-general in May 1811 and major-general in June. He was made a Knight Commander of the Tower and the Sword by Portugal and a Knight Bachelor by Britain for his services during the Napoleonic Wars.
