In 1858 Harding was elected to the Oregon State Legislature, but as Oregon had not yet been admitted to the Union, the assembly only met briefly before disbanding until 1859, when a special session was held and Harding served at the session. In 1860, he was elected again as a Democrat representing Marion County. At the next session of the legislature Harding was elected as Speaker of the Oregon House of Representatives, and this would be his final session in the state legislature.