[7] After being seconded for service with the Egyptian Army in January 1893,[8] he served in Sudan in the Dongola Expedition in 1896 as a staff officer to Major General Sir Herbert Kitchener, and was present at the Battle of Ferkeh and the operations at Hafir.

[9] In 1899, he took part in the final defeat of the Khalifa as Assistant Adjutant general in charge of Intelligence, and was mentioned in despatches (dated 25 November 1899) by Colonel Wingate with the following words: I cannot speak in sufficiently strong terms of the excellence of the services performed by this officer.

[12] During the Second Boer War Colonel Mahon led a flying column, 2,000 strong, consisting mainly of South African volunteers from Kimberley, which came to the Relief of Mafeking.

In April 1904, after serving on half-pay, took command of a second class district in India, for which he was promoted to substantive colonel and re-promoted to temporary brigadier general while holding the appointment.

[22] Furthermore, Hamilton chose to select Beauvoir De Lisle as the new commander of IX Corps, believing Mahon was not up to the task.

[22] In September he moved with the division to be head of the British Salonika Army to support Serbia at the onset of the Macedonian campaign.

The most valuable furniture had been removed to Dublin after the destruction of Palmerstown, the residence of Lord Mayo, another Kildare member of the Irish Senate, the previous month.