The 6th Division is an active division of the British Army, which has been raised numerous times as needed over the last 200 years. It was first established by Lieutenant-General Arthur Wellesley in 1810, for service in the Peninsular War as part of the Anglo-Portuguese Army. Over the following four years, the division took part in numerous battles and sieges. Notably, on 22 July 1812, the division was heavily engaged during the Battle of Salamanca and suffered the most casualties of any allied formation in that battle. Following the invasion of France, the formation played a prominent role in the 1814 Battle of Toulouse where it assaulted and seized numerous French redoubts protecting the city. While successful, the formation suffered heavy losses from the fighting. This battle marked the end of the Peninsular War and the War of the Sixth Coalition, and the division was broken-up. It was reformed and active for most of the following year, during the War of the Seventh Coalition; held in reserve at the beginning of the Battle of Waterloo, it was committed in the evening to bolster the centre-left of the British line and suffered heavy casualties in the process.

The Anglo-Portuguese Army was the combined British and Portuguese army that participated in the Peninsular War, under the command of Arthur Wellesley. The Army is also referred to as the British-Portuguese Army and, in Portuguese, as the Exército Anglo-Luso or the Exército Anglo-Português.