William McNally was born in Youghal, County Cork, on 21 May 1897, the son of Peter and Mary McNally, and joined the Royal Navy as a Boy Artificer on 3 January 1913. On completion of his five-year apprenticeship, he served in the battleship HMS CENTURION, HMS DELPHINIUM and HMS CATTISTOCK until 31 December 1919.

He joined submarines as an Engine Room Artificer Third Class on 30 November 1920 and served in HMS K14, HMS K26, HMS K6 and HMS L25. William McNally was promoted to Acting Warrant Engineer on 1 October 1926 and was appointed to HMS L5 as Engineer on 27 March 1927. An appointment HMS ROVER as the Engineer followed on 15 December 1931. William McNally was appointed to HMS STURGEON as Engineer and then HMS L23 as the Engineer on 26 July 1936. His next appointment was to HMS PROTEUS as the Engineer on 9 February 1938. William McNally was promoted to Commissioned Engineer on 1 October 1938. He was reappointed to the Submarine Depot Ship HMS AMBROSE at Dundee on 11 April 1940.

He was next appointed HMS TALISMAN as the Engineer on 2 April 1942. TALISMAN sailed from Gibraltar on 10 September 1942, heading for Malta where she was due on 18 September 1942. There was a report of a sighting of a U-boat off Algeria on 14 September but there was no further contact from the submarine. HMS TALISMAN is presumed to have been lost with all hands in an Italian minefield off Sicily on 17 September.

William McNally was the husband of Margaret Jane McNally. He is commemorated on the Portsmouth Naval Memorial on Panel No. 62 Column No. 2.