William was born on 28 June 1900 in Lesmahagow, Lanarkshire, the third child of Robert And Elizabeth (née Sandlands) Weir, the couple already had two daughters Rebecca (1905) and Cecilia (1897) all born and living in Lesmahaghow.

William Miller Weir joined the Royal Navy on Tuesday 31 October 1916 as a Boy Second Class with his service documents showing previous occupation as miner and age on entry 16 years and 4 months. He joined HMS POWERFUL the Boy Training Ship berthed in Devonport dockyard on 31 October for four months basic training and left on the 16 March 1917 for HMS GANGES, a shore establishment at Shotley, Suffolk. On the 9 May he was selected for Telegraphist and made up to Ord Tel, on 19 December, the day he left GANGES for HMS VICTORY 1 in Portsmouth. After one month in VICTORY he had a draft across Portsmouth harbour to HMS DOLPHIN on 22 January 1918 and was there confirmed as Telegraphist on 28 June. Two days later he was drafted to HMS MAIDSTONE based in Harwich for HMS L10.

L10 was hit and sunk by gunfire while on patrol in the Heligoland Bight area of the North Sea on 3 March 1918 with the loss of all 39 of her crew members. Telegraphist William Weir died with his shipmates.