William Arnett (1939–2020) was an American art collector.
William Arnett may also refer to:
W. David Arnett (born 1940), American astrophysicist Will Arnett (born 1970), Canadian-American actor and comedian
See also William Arndt (born 1993), American Canadian football player William Arnott (disambiguation) William Barnett (disambiguation) William Garnett (disambiguation) William Harnett (1848–1892), American painter