William Patrick 1 Kelly was born in Glasgow, Lanarkshire, Scotland on 19 June 1888. He was the son of Irish Roman Catholic parents William Kelly (b. 1862), a merchant tailor, and Annie Curran (b. 1862), natives of Co Tyrone who had married around 1885.
He had four siblings: Peter (b. 1886), Rosina (b. 1890), Annie Marie Elizabeth (b. 1896) and Adrian Joseph (b. 1899).
William first appears on the 1891 Scottish census. At the time his father was absent but he, his mother and siblings were living at 230 Paisley Road, Kinning Park, Govan, Glasgow along with his maternal grandparents Peter and Annie Curran. His mother was described as a housekeeper. He and his family moved to their native Ireland sometime before 1897 and settled in Dublin where his father ran a tailor and outfitter shop. There is no sign of the family on the 1901 census.
William was educated at the Christian Brothers' School in Dublin and Skerry`s Commercial College, Dublin. He served a three year apprenticeship with T. E. Brunker Electrical Engineers in Dublin and stayed with them until 1911. On the 1911 census of Ireland William and his family are living at 1 Claude Road, Drumcondra, Glasnevin in Dublin City. William, like his brother Peter, is described as an electrical engineer. In January 1912 he joined Harland & Wolff and was engaged upon electrical work aboard Titanic. In a letter to a friend, dated 10 March 1912, he described the anti-Catholic prejudice and vitriol that he and his like endured in the shipyard, and Belfast in general at the time. He was appointed as assistant electrical engineer aboard the ship; it would be his first working sea voyage.
When William signed on to the Titanic, in Southampton, for her maiden voyage, he gave his address as 1 Claude Road, Dublin. As assistant electrician he could expect monthly wages of £8.
William Kelly died in the disaster. His body, if recovered, was never identified.