After graduating from Albany Law School, William Freeman Vilas, enlisted in the Union Army during the Civil War. He was captain and later lieutenant colonel of the 23rd Wisconsin Volunteer Infantry Regiment.

After the war he became a Professor of Law at the University of Wisconsin-Madison. Vilas also served as a member of the Wisconsin State Assembly until 1885 when he was appointed to Postmaster General and later Secretary of the Interior by President Grover Cleveland.

From 1891 to 1897 Vilas was a member of the United States Senate, in which he was active in repealing the silver purchase clause of the Sherman silver Purchase Act. In the 1896 Democratic National Convention, Vilas was a delegate and then became one of the chief leaders of the National Democratic Party.