William Duncan may refer to:
Arts, entertainment, and literature
William Cary Duncan (1874–1945), American playwright and author
William Duncan (actor) (1879–1961), Scottish-born actor and director of film serials
W. Murdoch Duncan (1909–1976), Scottish crime thriller author
William "Willie" Duncan (born 1955), guitarist and singer with the Spider Murphy Gang
Medicine and science
Sir William Duncan, 1st Baronet (died 1774), Scottish physician
William Duncan (American physician) (1840–1900)
William Henry Duncan (1805–1863), English doctor and Britain's first Chief Medical Officer
William Jolly Duncan (1894–1960), Scottish physicist
Politicians
William Addison Duncan (1836–1884), U.S. representative from Pennsylvania
William C. Duncan (1820–1877), brewer, politician, and mayor of Detroit, Michigan
William Duncan (Maryland politician) (1871–1925), American politician and lawyer
William Garnett Duncan (1800–1875), U.S. representative from Kentucky
William H. Duncan, American diplomat
Sports
Art Duncan (William James Arthur Duncan, 1891–1975), Canadian ice hockey professional and World War I flying ace
Bill Duncan (1880–?), Scottish footballer
William Butler Duncan (1862–1933), American yachtsman and adoptive son of William Butler Duncan (below)
William Dow Duncan (1892–1961), New Zealand rugby player
Bill Duncan (Jockey) (1900-1983), Australian jockey
William Duncan (Australian cricketer) (1912–1943), Australian cricketer
William Duncan (footballer) (1913–1975), Scottish association football player
William Duncan (New Zealand cricketer) (1933–2008), New Zealand cricketer
Willie Duncan (rugby union) (William Robert Duncan, born 1957), Irish international rugby union player from Northern Ireland
Billy Duncan, Northern Ireland boxer
Others
W. Butler Duncan (1830–1912), Scottish-American banker and railroad executive, adoptive father of William Butler Duncan
William Augustine Duncan (1811–1885), Scottish journalist and colonial official
William Barr McKinnon Duncan (1922–1984), Scottish-born director of Imperial Chemical Industries, chief executive of Rolls-Royce
William Duncan (missionary) (1832–1918), English-born Anglican missionary
William Duncan (philosopher) (1717–1760), Scottish natural philosopher and classicist
William fitz Duncan (1090/1094–1147), Scottish prince and general
William Wallace Duncan (1839–1908), American bishop of the Methodist Episcopal Church, South