He moved to Springfield, Illinois in 1853, where he studied law with Stuart & Edwards and was admitted to the bar in 1855.

[1] In 1870, he lost renomination, falling one vote short at a party convention that lasted 186 ballots over five days.

[6] He resigned in 1883 to take office as a US senator; Lieutenant Governor John Marshall Hamilton assumed the governorship in his place.

He believed that only the federal government had the power to force railroads to provide fair treatment to all of its customers, large and small.

This was because corporations, such as Standard Oil, had corrupted many of the railroads' officials into providing them with rebates, and as a whole, the companies in question were more powerful than any state government.

Together with Congressman Isaac S. Struble, Cullom pushed the Cullom-Struble Bill, whose sanctions against polygamy included exclusion of the Utah Territory from statehood.

[8] Cullom was appointed by President William McKinley in July 1898 to the commission created by the Newlands Resolution to establish government in the Territory of Hawaii.