Watts was born on 14 February 1858, the son of the Reverend R.L.R. Watts, the vicar of Wisbech. He was educated at The King's School, Peterborough and at Tours, and was commissioned as a second lieutenant into the 14th Regiment of Foot in April 1880 (the regiment changed name to become The Prince of Wales's Own West Yorkshire Regiment later the same year). He served with the regiment for 30 years, during which he was promoted to lieutenant on 1 July 1881, captain on 6 March 1889, and major on 20 March 1899. Following the outbreak of the Second Boer War in late 1899, he served with the 2nd battalion of his regiment in South Africa 1899-1902. He took part in operations in the Natal, including the battles of Vaal Krantz (6-7 February 1900) and the Tugela Heights and Pieter's Hill (14-27 February 1900) leading to the Relief of Ladysmith. In the following months he served in the Natal, and from July to November 1900 in the Transvaal. During the war he was mentioned in despatches five times and received the brevet promotion to lieutenant-colonel on 29 November 1900. He was appointed 2nd in command of his battalion on 7 March 1902, and after peace was declared the following month, left South Africa on board the SS "Bavarian" to arrive in the United Kingdom in June 1902.