Cameron was commissioned as an officer in the Grenadier Guards on 5 September 1896, and promoted to lieutenant on 8 September 1898. He served in South Africa 1899-1900 during the Second Boer War, where he was part of the Kimberley relief force, and was wounded at the Battle of Belmont (November 1899).[4] He was in South Africa for the end of the war, and was invalided home in July 1902, when he left Cape Town on the SS Canada, returning to Southampton.[5] Lochiel was back with his regiment the same month and promoted to Captain.[6]
In 1914, Lochiel (who was then commanding officer of the 3rd Reserve Battalion of the Queen's Own Cameron Highlanders) was asked by Field Marshal Herbert Kitchener, 1st Earl Kitchener to raise several battalions of infantry; Lochiel agreed, on the condition that he would be Colonel; one of these became the 5th Service Battalion of the regiment, which saw distinguished service on the western front as part of the 9th (Scottish) Division. His brothers, Allan and Archibald Cameron, also served in the Cameron Highlanders but were both killed in 1914 and 1917.[7][8] Their deaths and those of the many others serving under his command deeply affected him.[1] He was invalided home, but resumed command of the 3rd Battalion in January 1918, when it was in Ireland.[9]
Lochiel travelled to North America several times: firstly with his wife in 1913, and again in 1923, returning in 1924. He was also a passionate advocate of the Scottish Gaelic revival and served as Chief, Gaelic society of Inverness (although he could not speak the language himself).[14] He was also the first Cameron Chief to organise Clan Cameron gatherings, which took place for the first time in 1938.[14]
During the Second World War, he vacated his residence of Achnacarry to the military for 25,000 soldiers to undergo elite commando training between 1942 and 1945. Achnacarry, transformed into the Commando Basic Training Centre, was known to the soldiers as "Castle Commando".[15]