William Leahy may refer to:
- William D. Leahy (1875–1959), American naval officer, diplomat, and chairman of the Joint Chiefs of Staff in World War II
- William Leahy (DCM) (1893–1918), Australian World War I Distinguished Conduct Medal recipient
- William Harrington Leahy (1904-1986), American naval officer
- F. William Leahy (1908–1973), known as Frank Leahy, American football coach
- William P. Leahy (born 1948), President of Boston College