After participating in many of the colonial wars throughout the remainder of the 19th century, all three regiments fought in the South African, or Boer War.

Here the Royal Irish Rifles were joined by volunteers from the London Irish, raised in 1860 as the 28th Middlesex (London Irish) Rifle Volunteer Corps, and Militia. A Militia battalion of the Royal Irish Rifles - the 5th or South Down - was one of the few Militia battalions to serve in South Africa. In 1827 the 87th had become a fusilier regiment and renamed The Royal Irish Fusiliers, whose nicknamed was "the Faughs."

Battalions of Inniskillings and Faughs served in General Hart's famous Irish Brigade. The bravery of these regiments - together with that of her other Irish regiments - inspired Queen Victoria to call for the raising of a regiment of Irish Foot guards. The Queen also ordered that, in future, all Irish regiments should wear shamrock on St Patrick's Day.