Born at Barrackpore, Bengal, in 1852, and is the son Major Henry G Mainwaring, late of the 1st Bengal Native Infantry. He was educated privately, and in 1872 was gazetted to the 24th Regiment He served with his regiment in the Kaffir War in 1877-8, including the operations against the Galekas; and also served throughout the Zulu War, afterwards surveying the battlefield of Isandhlwana. He acted as Transport Commissariat and Ordnance Officer, and was on the Camp escort of Lord (then Sir Garnet) Wolseley at Ulundi. Whilst on a big game shooting expedition in Somaliland, he surveyed some hitherto unexplored ground along the southern boundary of Abyssinia. Colonel Mainwaring commanded the 1st Battalion South Wales Borderers (24th Regiment) from 1896-1901. Recreations: Shooting and fishing, having won several prizes at rifle meetings, amongst others, The All Comers at the Caird Rifle Meeting in 1894. He married, Feb 2, 1889, Henrietta, daughter of Henry Wigan.