Blackmore's father, Edwin Gordon Blackmore (1837–1909), an Englishman from Bath, the son of a doctor, had fought as a volunteer in the "Maori Wars" with the Taranaki Rifle Volunteer Corps from 1863 to 1864, and had moved to South Australia and had established himself in Adelaide.

His older brother Quartermaster Sergeant George Edward Blackmore (No.85), had served in the Boer War with the Third South Australian Citizens' Bushmen Contingent.

[7] Recruited from Melbourne Grammar School, when still a student there, he played on the forward line, and kicked four goals from five shots in his first senior game against St Kilda, at the Junction Oval on 2 September 1905.

Prior to his enlistment he was farmer and grazier, working with his brother, John Coleridge Blackmore, at Wattamondara, near Cowra, in New South Wales.

On 21 December, having finished his basic training, he was promoted from Trooper to Lance Corporal; and, on that same day, as part of the 6th Light Horse Regiment, A Troop, A Squadron, he embarked from Sydney on board HMAT Suevic (A29).

He was immediately sent to Cardiff, Wales, in the UK to recover and, once he was well enough to do so, he returned to his unit, in Egypt, in January 1916.