Born the son of Colonel Charles James Briggs, JP, DL, Brigg's education took place largely abroad, including periods in France and Germany. He was commissioned into the 1st King's Dragoon Guards on 30 January 1886 and served as ADC to the General Officer Commanding Egypt from 1892 to 1893. Promoted to captain on 1 March 1893, he became Adjutant of the 1st Dragoon Guards in November 1894 and Brigade Adjutant of the 4th Cavalry Brigade in April 1897. He served in the Second Boer War as Brigade Major of the 3rd Cavalry Brigade and was wounded at the Battle of Magersfontein (December 1899). He received a brevet rank as major on 29 November 1900, and was promoted to the substantive rank of major on 14 June 1902. Following the end of the war in June 1902, he left Cape Town on the SS "Sicilia" and returned to Southampton in late July. For his services during the war, he received a brevet promotion to lieutenant-colonel in the South African Honours list published on 26 June 1902. Reported to be medically unfit for foreign service after his return from the war, he was on 1 November 1902 appointed in command of a provisional regiment of Lancers, stationed at Ballincollig. He went on to command the 1st Imperial Light Horse and then a Mobile Column, before transferring to the 6th Dragoons in July 1904.