William Rennie may refer to:

• William Rennie (Victoria Cross) (1822–1887), Scottish recipient of the Victoria Cross
• William Rennie (horticulturist) (1835–1910), scientific farmer and seed merchant in Ontario
• Willie Rennie (William Cowan Rennie, born 1967), Scottish politician
• William J. Rennie (1891–1964), American football and basketball coach
• William Hepburn Rennie, British colonial official in Hong Kong and St. Vincent

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