His family moved to Kent in 1906 and then to Derbyshire where he attended Chesterfield Grammar School. His father was a school master at Netherthorpe Grammar School in Staveley. He went to Trinity College, Cambridge in 1923 where he studied Mathematics, later gaining a PhD in 1929 under Ralph H. Fowler.
From 1930 he lectured in Mathematics at the University of Edinburgh. During his time in Edinburgh (in 1931) he was elected a Fellow of the Royal Society of Edinburgh. His proposers were Sir Edmund Taylor Whittaker, Sir Charles Galton Darwin, Edward Copson and Charles Glover Barkla. He won the Society's Keith Medal (jointly with Edward Copson) for the period 1939–41.
In the Second World War he was co-opted onto the Admiralty Operational Research Group. After the war, he joined the mathematics department at Royal Holloway College in 1944 (the McCrea Building on Royal Holloway's campus is named after him). He was elected a Fellow of the Royal Society of London in 1952.
In 1965, McCrea created the astronomy centre of the physics department at the University of Sussex.
In 1933 he married Marian Core (d. 1995) and had three children.
In 1928, he studied Albrecht Unsöld's hypothesis, and discovered that three-quarters of the Sun is made of hydrogen, and about one quarter is helium, with 1% being other elements. Previous to this many people thought the Sun consisted mostly of iron. After this, people realised most stars consist of hydrogen.
McCrea was president of the Royal Astronomical Society from 1961 to 1963 and president of Section A of the British Association for the Advancement of Science from 1965 to 1966.
- Mestel, L.; Pagel, B. E. J. (2007). "William Hunter McCrea. 13 December 1904 -- 25 April 1999: Elected FRS 1952". Biographical Memoirs of Fellows of the Royal Society. 53: 223. doi:10.1098/rsbm.2007.0005.
- Mestel, Leon (30 April 1999). "Obituary: Sir William McCrea – The Independent". London. Retrieved 20 July 2011.
- Biographical Index of Former Fellows of the Royal Society of Edinburgh 1783–2002 (PDF). The Royal Society of Edinburgh. July 2006. ISBN 0-902-198-84-X.
- McCrea, Monthly Notices of the Royal Astronomical Society, 128:147, 1964 doi:10.1093/mnras/128.2.147 (This paper has over 400 citations.); Carney, Latham, and Laird, The Astronomical Journal, 129:466–479, 2005; Perets, and Fabrycky, The Astrophysical Journal, 697:1048–1056, 2009