Knowland joined the Alameda Good Government Club in early 1895. He was appointed, in 1896, to the Alameda Library Board of Trustees. He was sought by the Alameda County Central Committee of the Republican Party to run for the State Assembly in 1898. Asked later in life why he entered politics, Knowland would reply, "I was one of these young men that took to politics and was interested." He was a member of the State Assembly from 1899 to 1903. Knowland chaired the Assembly committee to investigate the conditions of the Chinese slave women in San Francisco. He served in the California State Senate from 1903 to 1904, when he resigned, having been elected as a Republican to the Fifty-eighth Congress to fill the vacancy caused by the resignation of Victor H. Metcalf. President Theodore Roosevelt had appointed Metcalf to be Secretary of Commerce and Labor.