Samuel Sigman attended law school at the University of Wisconsin and at George Washington University. In 1927 he passed his bar examination and moved to Appleton to join his brother's law firm. During the late 1920s and early 1930s, he served as secretary of the board of trustees of Appleton Labor College, and acted as counsel for the Appleton Trades and Labor Council, for the Fox River Valley Home Merchants Association, and for the Wisconsin Federation of Commercial Fishermen.
From his school days, Sigman was active in the Wisconsin Progressive movement. Even before his graduation from law school he served as secretary to George Schneider, Progressive Republican congressmen from the ninth district. In 1928 he was campaign secretary for Robert M. La Follette, Jr. Sigman made several campaigns for the district attorneyship of Outagamie County, and in 1934 finally succeeded in becoming the first Progressive to be elected to office in Outagamie County. He helped to organize and was the first chairman of the Farmer-Labor Progressive League. Later he served on the executive board of the Farmer-Labor Progressive Federation (later renamed the Progressive Party Federation).
During the 1940s, with the slow decline of the Progressive movement in Wisconsin, Sigman become one of the many Progressives to transfer allegiance to the Democratic Party. In later years Sigman was active in the human rights movement, working with the Anti-Defamation League of B'nai B'rith, and acting as secretary-treasurer of the Appleton Interfaith Committee on Tolerance and Understanding (affiliated with the Governor's Commission on Human Rights).
