William Weir may refer to:
- William Alexander Weir (1858âÂÂ1929), Quebec lawyer and politician
- William Weir (architect) (1865âÂÂ1950), Scottish restorer of historic buildings
- William Weir, 1st Viscount Weir (1877âÂÂ1959), Scottish industrialist
- William Weir, 3rd Viscount Weir (born 1933), British peer and businessman
- William Gilbert Weir (1896âÂÂ1971), Canadian politician
- Bill Weir (born 1967), co-anchor of Good Morning America Weekend Edition
- Bill Weir (footballer), Australian rules footballer
- William Weir (aviator) (1891âÂÂ1917), World War I flying ace
- William Weir (trade unionist) (1868âÂÂ1926), British coal miner and politician
- Dr. William Weir, fictional character in Event Horizon (film)