In 1800, he received his majority, and in 1804 he became lieutenant colonel of the 7th. In command of this regiment he sailed to join Lieutenant-General Sir David Baird at Corunna in 1808, and took part in Lord Henry Paget's cavalry fights at Sahagún and Benavente. During the retreat of Lieut-General Sir John Moore's army the 7th were constantly employed with the rearguard. Vivian was present at the Battle of Corunna, and returned with the remainder of the army to England. It was not until September 1813 that the 7th returned to the Peninsula. On 24 November, Vivian (now colonel and aide-de-camp to the Prince Regent) was appointed to command a light cavalry brigade (13th and 14th Light Dragoons) under Rowland Hill, 1st Viscount Hill in Wellington's army. With this corps he served at the Battle of the Nive (9–13 December).