In the British Army, a Brigade Major was the Chief of Staff of a brigade. He held the rank of Major and was head of the brigade's "G - Operations and Intelligence" section directly and oversaw the two other branches, "A - Administration" and "Q - Quartermaster". Intentionally ranked lower than the Lt-Colonels commanding the brigade's combat battalions his role was to expand on, detail and execute the intentions of the commanding Brigadier.
During the Great War, the Brigade Major was reportedly "a key personality who affected the health and happiness of the battalions."[1] as he would be in most frequent contact with the frontline troops and held responsibility for the planning of brigade operations.
In 1913 Staff Captains of Artillery in the British Army were re-styled as Brigade Majors to bring them into line with Cavalry and Infantry practice. The title is however no longer used except in the Household Division and in divisional level artillery HQs.
The practice of using Brigade Majors has continued in some Commonwealth armies such as those of India.