Isaac Siegel (April 12, 1880 - June 29, 1947) was a U.S. Representative from New York.
He was born in New York City and attended the public schools. Siegel was graduated from New York University School of Law in 1901 and was admitted to the bar on May 26, 1902. He commenced practice in New York City thereafter and was appointed special deputy attorney general for the prosecution of election frauds in 1909 and 1910. Siegel was elected as a Republican to the Sixty-fourth and to the three succeeding Congresses (March 4, 1915-March 3, 1923). He was chairman of the Committee on the Census (Sixty-sixth and Sixty-seventh Congresses). He was not a candidate for renomination in 1922. During the First World War, he was a member of the overseas commission which visited France and Italy during July and August 1918. He was also delegate to the Republican National Conventions in 1916, 1920, 1924, and 1936. In September 14, 1940, Siegel was appointed to the bench and served as justice of the domestic relations court of New York City until his death in that city.