William Nelson may refer to:
- Billy Nelson (athlete) (William Andrew Nelson, born 1984), American steeplechaser
- William Nelson (governor) (1711–1772), American colonial governor of Virginia
- William Nelson (British judge) (born c. 1981), British district judge
- William Nelson (MP) (c. 1462–1525), member of parliament for the City of York
- William Nelson (New York politician) (1784–1869), U.S. congressman for New York
- William Nelson (Wisconsin politician) (1839–1913), member of the Wisconsin State Senate
- William Nelson (wrestler), American wrestler who won a bronze medal at the 1904 Olympics
- William Nelson, 1st Earl Nelson (1757–1835), elder brother of Horatio Nelson, 1st Viscount Nelson
- William "Bull" Nelson (1824–1862), Union army general in the American Civil War
- William E. Nelson (died 1991), murdered by his wife Omaima Nelson
- William G. Nelson (fl. 1980s–2020s), American cancer researcher and professor
- Harold Nelson (athlete) (William Harold Nelson, 1923–2011), New Zealand runner
- William L. Nelson (politician) (1875–1946), U.S. congressman for Missouri
- William L. Nelson (Medal of Honor) (1918–1943), World War II Medal of Honor recipient
- William Lambie Nelson (1807–1887), member of the Queensland Legislative Assembly
- William T. Nelson (1908–1994), U.S. Navy rear admiral
- William Rockhill Nelson (1841–1915), American journalist and publisher
- William Nelson (industrialist) (1843–1932), New Zealand farmer and industrialist
- William Nelson (inventor) (died 1903), American inventor killed by own invention