Sidney was born in Wolverhampton in 1893, the son of John and Mary Dark. In 1901 and in 1911, he was living with his parents at 226 Lea Road, Wolverhampton, along with his sisters Evelyn, Elsie May and Amy Elizabeth, and brother Geoffrey. Sidney was a press tool maker.
On 22 October 1915, he enlisted with the Army Service Corps (number 134524). By this date, his trade was a turner. He served in France from 21 November 1915 until 18 January 1919.
Sidney married Hannah Tanswell in 1919, and they had two children, Clifford S. and Hylda M., in 1920 and 1924. Sidney died in Wolverhampton on 27 May 1939 at the age of 45. By the date of his death, his address was 56 Osborne Road, Penn, and the value of his effects was £971 9s 10d. His First World War service was honoured on the memorial from Penn Road Wesleyan Chapel.