Sylvester J. Ryan (September 10, 1896 – April 10, 1981) was a United States federal judge.
Born in New York, New York, Ryan attended the City College of New York and an LL.B. from Fordham University School of Law in 1917. He was in private practice in New York City from 1918 to 1924. He was a Chief assistant and acting district attorney of Bronx County, New York from 1924 to 1947.
Ryan was a federal judge on the United States District Court for the Southern District of New York. Ryan received a recess appointment from President Harry S. Truman on November 1, 1947, to a seat vacated by Francis G. Caffey. Formally nominated on November 24, 1947. He was confirmed by the United States Senate on December 18, 1947, and received his commission on December 20, 1947. He served as chief judge from 1959-1966. He assumed senior status on January 3, 1973. Ryan served in that capacity until April 10, 1981, due to his death.
He died in New York, New York.