William Hewlett may refer to:
- Bill Hewlett (1913–2001), American engineer and co-founder of the Hewlett-Packard Company
- Will Hewlett (1876–1921), Welsh trade unionist and socialist activist
- William Hewlett (regicide), officer involved in the execution of Charles I of England in 1649
- W. H. Hewlett (1873–1940), Canadian composer, organist, and choir conductor