| John William Clancy | |
| Office: | Senior Judge of the United States District Court for the Southern District of New York |
| Term Start: | April 3, 1959 |
| Term End: | March 2, 1969 |
| Office1: | Chief Judge of the United States District Court for the Southern District of New York |
| Term Start1: | 1956 |
| Term End1: | 1959 |
| Predecessor1: | William Bondy |
| Successor1: | Sylvester J. Ryan |
| Office2: | Judge of the United States District Court for the Southern District of New York |
| Term Start2: | June 22, 1936 |
| Term End2: | April 3, 1959 |
| Appointer2: | Franklin D. Roosevelt |
| Predecessor2: | Seat established by 49 Stat. 1491 |
| Successor2: | Charles Miller Metzner |
| Birth Name: | John William Clancy |
| Birth Date: | 24 February 1888 |
| Birth Place: | New York City, New York |
| Death Place: | New York City, New York |
| Education: | Fordham University (B.A.) Fordham University School of Law (LL.B.) |
John William Clancy (February 24, 1888 – March 2, 1969) was a United States district judge of the United States District Court for the Southern District of New York from 1936 to 1969 an its Chief Judge from 1956 to 1959.
Born in New York City, New York, Clancy received a Bachelor of Arts degree from Fordham University in 1909 and a Bachelor of Laws from Fordham University School of Law in 1912. He was in private practice in New York City from 1912 to 1936.
On June 15, 1936, Clancy was nominated by President Franklin D. Roosevelt to a new seat on the United States District Court for the Southern District of New York created by 49 Stat. 1491. He was confirmed by the United States Senate on June 20, 1936, and received his commission two days later. He served as Chief Judge from 1956 to 1959, assuming senior status on April 3, 1959. Clancy served in that capacity until his death in New York City on March 2, 1969.