The 91st Regiment was officially formed in 1793 by John Campbell 5th Duke of Argyll. However it had been formed and disbanded three times prior to this date from 1759. The Regiment was initially numbered as the 98th Argyllshire Highlanders but renumbered as the 91st in 1798. The Regiment was first in action in South Africa to capture the Cape of Good Hope from the Dutch and remained garrisoned there for 7 years. In 1808 the Regiment was deployed to Portugal and acted as a rear guard action against Napoleon’s Army during the evacuation of Corunna which signalled the start of the Peninsular War. The 91st was then deployed on the unsuccessful Walcheren Campaign before returning to Spain to fight at the Battles of Vittoria, Sorauren, Nivelle and Bayonne as well as at the Battle of Toulouse which ended the Peninsular war in 1814. In 1871 Queen Victoria’s fourth daughter Princess Louise married John Campbell, Marques of Lorne, and heir to the Duke of Argyll. The 91st provided the Guard of Honour at the wedding and in 1872 Princes Louise became their Colonel-in-Chief. In recognition of this the Regiment was renamed the 'Princess Louise's Argyllshire Highlanders'. The Regiment then moved to Inverness on its first Scottish tour of duty in 80 years and then returned to South Africa during the Zulu Wars 1879.
In 1881 during the Childers Reforms the 91st were amalgamated with the 93rd (Sutherland Highlanders) Regiment of Foot becoming the 1st Battalion, Princess Louise's Argyll and Sutherland Highlanders.