Upon the death of Terence's older brother Archibald, Earl of Ava at the Siege of Ladysmith in the Second Boer War in 1900, he became the heir and assumed the courtesy title Earl of Ava himself before succeeding his father in 1902. Lord Dufferin died from pneumonia on 7 February 1918 and was buried at the Dufferin ancestral seat of Clandeboye, County Down.