Paterson was commissioned a second lieutenant in the Prince Albert's (Somersetshire Light Infantry) on 16 February 1898, and was posted with the regiment's 2nd Battalion in South Africa during the Second Boer War (1899-1902). He was promoted to lieutenant on 7 January 1900, during the advance to relieve Ladysmith, where he took part in the battles of Spion Kop (20-24 January 1900) and the Tugela Heights (February 1900). From April 1900 until 1901 he served at the base depot. After the end of the war in June 1902, Paterson left Cape Town in the "SS Bavarian" in August, returning to Southampton the following month.