 Fullmer crossed the plains to Utah with his family in 1848 and settled in Davis County, where he was actively involved in the political affairs of the territory and assisted in the drafting of a constitution for the provisional State of Deseret and the Utah Territory.Fullmer briefly served in the Utah Territorial House of Representatives from Davis County, while his brother, David, served in the House for Salt Lake County.Fullmer again served as a missionary from 1852 to 1855, this time to England.