Williamson apprenticed and then practiced as a harness maker from 1866 to 1890.
During this time, he rose in local politics to county treasurer and clerk. In 1900, Williamson was elected Illinois Treasurer as a Republican, serving a two-year term. They settled in Sparta Township, Knox County, Illinois.
Moses helped on the family farm until he was twelve, when he went to work on a neighbor"s farm.
When he was fourteen, Williamson apprenticed as a harness maker in Wataga, Illinois. He trained for three years under Olsen & Gray, then worked a year as a journeyman.
Williamson then purchased Gray"s share of the partnership, then sold harnesses with Olsen from 1867 to 1879. He then purchased Olsen"s share, running the harness shop alone until 1890.
Williamson rose in Wataga politics, serving at various times as justice of the peace, town clerk, and councilman.
In 1884, he was named Secretary of the Republican County Central Committee, a role he held for at least 16 years. Williamson was elected Knox County Treasurer in 1886. In 1890, he left his harness shop to move to Galesburg, Illinois, to serve as Knox County Clerk.
He was elected to three consecutive four-year terms.
After co-founding the Swedish American Republican League of Illinois, Williamson was named its president in 1897. In 1900, Williamson was elected Illinois Treasurer, serving from 1901 to 1903.
Williamson married Mary Driggs on October 18, 1871. They had two surviving daughters: Addie and Nellie.
He died at his home in Galesburg on February 24, 1935, due to complications from broken hip.