Wilson fought in the Second Boer War as a corporal in the 2nd Queensland Mounted Infantry Contingent, serving in the advance to Johannesburg and Pretoria, the Battle of Diamond Hill and other actions. Commissioned in the 15th Light Horse Regiment in 1904, he trained with other future leaders of the Light Horse under Lieutenant Colonel Harry Chauvel. Promoted major in 1911, Wilson was second-in-command of the Moreton Regiment after his return to Brisbane. There he entered into a partnership with E. K. Tully to form one of Queensland's leading law firms.