Colleen McMahon (born 1951) is a Chief Judge of the United States District Court for the Southern District of New York. Born in Columbus, Ohio, McMahon received a B.A. from Ohio State University in 1973 and a J.D. from Harvard Law School in 1976. She was in private practice in New York from 1976 to 1995, except for a period from 1979 to 1980 when she was a speechwriter and special assistant to the Hon. Donald McHenry, the United States Permanent Representative to the United Nations. She was a judge on the New York Court of Claims, New York Supreme Court, from 1995 to 1998. On May 21, 1998, McMahon was nominated by President Bill Clinton to a seat on the United States District Court for the Southern District of New York vacated by John F. Keenan. McMahon was confirmed by the United States Senate on October 21, 1998, and received her commission the next day. She became Chief Judge on June 1, 2016.