The brigade was initially formed of four volunteer battalions from the Royal Fusiliers, primarily recruited from London.
The 17th was formed by the British Empire Club, a recruiting organisation chaired by General Sir Bindon Blood, Herbert Nield, the Conservative MP for Ealing, and Major-General Lionel Herbert. The Club was authorised to raise a battalion on 30 August; they had completed recruitment and moved into camp by 12 September, under the command of Colonel George Robert Harland Bowden MP. The 22nd was raised by the Mayor of Kensington, William Davison, and included two companies of volunteers from the borough as well as two of colonial volunteers from the King Edward's Horse. The 23rd and 24th "Sportsmen's Battalions" were raised by Mrs Cunliffe-Owen, daughter of Sir Philip Cunliffe-Owen, who offered to raise "a complete battalion of upper and middle class men, physically fit, able to shoot and ride, up to the age of forty-five"; in the event, she provided a second as well. The men of the 23rd and 24th were a varied group of British and Colonial adventurers, including engineers, fur trappers, big-game hunters, and athletes.
During training in England, the brigade was reinforced with the 1/5th Battalion, King's (Liverpool) Regiment, and the 1st Battalion, Royal Berkshire Regiment. The 99th Brigade was sent to France in November 1915 as part of 33rd Division, but was quickly transferred to the 2nd Division in exchange for a veteran brigade of regular and territorial troops. Many of its units were rotated out to other brigades at this point, and by the end of 1915 it consisted of:
The brigade remained on the Western Front with 2nd Division for the remainder of the war.