| Office: | Acting Judge Advocate General of the United States Army |
| President: | Rutherford B. Hayes |
| Term Start: | January 22, 1881 |
| Term End: | February 18, 1881 |
| Predecessor: | William McKee Dunn |
| Successor: | David Gaskill Swaim |
| Birth Date: | August 3, 1831 |
| Birth Place: | New Haven, Connecticut, U.S. |
| Death Date: | April 8, 1899 |
| Death Place: | Atlantic City, New Jersey, U.S. |
| Spouse: | Alice Worthington Winthrop |
| Parents: | Elizabeth Dwight (Woolsey) Winthrop |
| Relatives: | Theodore Winthrop (brother) |
| Education: | Yale University (A.B.) Yale Law School (LL.B.) |
| Allegiance: | United States of America Union |
| Branch: | United States Army Union Army |
| Serviceyears: | 1861 - 1895 |
| Rank: | Colonel |
| Unit: | 7th New York Militia 1st United States Sharpshooters |
| Commands: | Judge Advocate General of the Army |
| Battles: | American Civil War |
William Woolsey Winthrop (1831–1899) was acting Judge Advocate General of the United States Army from January 22, 1881, to February 18, 1881. He was the author of Military Law and Precedents. The United States Supreme Court has described him as "the Blackstone of military law."