In 1912, Knott was elected to the New York State Assembly as a Democrat, representing the New York County 25th District. He served in the Assembly in 1913. He was an alternate delegate to the 1916, 1924, 1928, and 1932 Democratic National Conventions, and served as a delegate to the 1936 and 1952 Democratic National Conventions. In 1917, he was elected Sheriff of New York County, and served as Sheriff from 1918 to 1922. In the 1922 United States House of Representatives election, he unsuccessfully ran as the Democratic candidate in New York's 14th congressional district. In 1922, he was elected chairman of the New York County Democratic Party Committee. He was still serving as chairman when he died.