In November 1932, he was elected to the State Assembly, where he served for serving two years. In 1934 he won election to the California State Senate, where he served for four years. He did not seek re-election in 1938 but remained active in the California Republican Party. He was also influential on the national scene, serving as the chairman of the executive committee of the Republican National Committee from 1940 to 1942. Knowland campaigned for Wendell L. Willkie, the unsuccessful Republican nominee for president in 1940.