Originally joining the Army in 1888 as a junior officer in the Leicestershire Regiment, Blackader's first active posting was in the late 1890s, when he served on attachment to the West African Frontier Force, closely followed by service during the Boer War, where he commanded a company at the defence of Ladysmith. An efficient and well-regarded administrator, he commanded a series of detached stations in addition to his regimental duties for the next ten years, eventually rising to take command of the 2nd Battalion, Leicestershire Regiment, in 1912. On the outbreak of the First World War, he commanded his battalion on the Western Front as part of an Indian Army formation; when his superior officer was promoted in early 1915, Blackader succeeded him as commander of the brigade, and led it through the Battle of Neuve Chapelle and the Battle of Loos.