His energy, devotion, and quiet cheerfulness helped to expedite the fatal enterprise, and at the end of the disastrous campaign he was promoted to brevet colonel (25 August 1885), receiving the Order of the Medjidieh (3rd class). On 30 December, as chief staff officer of a combined British and Egyptian force, he took part in the battle of Ginnis, when a large army of the Khalifa, endeavouring to invade Egyptian territory, was defeated with great loss. For his services Ardagh was mentioned in despatches. On 17 December 1886 he was promoted to a regimental lieutenant-colonel, and on 26 January 1887 he was gazetted a colonel on the staff. In November 1887 Ardagh returned to London as assistant adjutant-general for defence and mobilisation at the war office, and inaugurated schemes of mobilisation for over-seas service, and for local home defence. From April 1888 to 1893 he was aide-de-camp to the Commander-in-Chief of the Army. In October 1888 he became, with the permission of the War Office, private secretary to the Viceroy of India, the Marquis of Lansdowne. Apart for a period of absence through illness in 1892, he remained with Lord Lansdowne through his term of office. He returned to England in May 1894, after serving briefly under Lansdowne's successor, Lord Elgin. He was made a Companion of the Order of the Indian Empire in 1892, and a Knight Commander of the Order of the Indian Empire in 1894. Ardagh served as commandant of the School of Military Engineering at Chatham from April 1895 until April 1896, when he returned to the War Office to serve as Director of Military Intelligence. He was promoted to major-general on 14 March 1898. On the outbreak of the South African War in October 1899, Ardagh's department was criticized for providing poor intelligence on the military strength and preparations the Boers had made for war. In response, Ardagh, in spite of a limited staff and inadequate funds, compiled a full statement of the numbers and military resources of the Boer forces, estimating that the defence of the British colonies would require 40,000 men, while to carry the war into the enemy's country would require 200,000. Copies of this report were eventually laid before both houses of parliament at Ardagh's request. Meanwhile a copy of "Military Notes on the Dutch Republic", a study prepared in secret by Ardagh's intelligence branch, fell into the hands of the Boers after the Battle of Talana Hill on 20 October 1899, and was later published.