William Sivier was born at Westbourne Street Mews, Paddington, London 1, England on 23 December 1888, being baptised on 19 May the following year in St James' Church, Paddington.
He was the son of a domestic coachman, Thomas William Sivier (b. 1853), a native of the Isle of Wight, and Annie Woodcock (b. 1861), who hailed from Retford, Nottinghamshire. The couple had married in Derbyshire in 1881 and had three more children (that are known of) besides William: Ellen (b. 1885), Thomas (b. 1886) and Henry (b. 1891).
The family appear on the 1891 census living at 9 Westbourne Street Mews, an address he would reside at for the rest of his life. His mother died in 1893 aged 32 and his father was remarried in 1895 to Mary Jane Nicholl (b. 1870), a native of Stepney, London. William had gained a half-sibling, George (1896-1964) by the time the 1901 census had been conducted.
When he signed-on to the Titanic, on 6 April 1912, he gave his address as 9 Westbourne S. Mews, Paddington, (London). His last ship had been the St Louis. As a third class steward he received monthly wages of £3, 15s.
William Sivier died in the sinking. His body, if recovered, was never identified.
His father later lived in Croydon, Surrey and died in 1929. His stepmother died in 1951.