He was a member of the Minnesota Senate from 1927 until his resignation in 1929. He was elected as a Republican to the 71st and 72nd US Congresses, (March 4, 1929 – March 3, 1933) and was an unsuccessful candidate for renomination in 1932.
He resumed agricultural pursuits and was appointed executive assistant to the director of production, Division of Agricultural Adjustment Administration, in June 1933. He was director of the Production Division and assistant administrator from January 1934 through February 1935. He was appointed state administrator of the Minnesota Works Progress Administration in June 1935 and served until June 1938.
From 1939 through 1954 Christgau was state director of the Minnesota division of employment and security at St. Paul. He then served as president of the Interstate Conference Employment Security Agencies from 1947 to 1948; Director, Bureau of Old Age and Survivors Insurance, Social Security Administration, from 1954 to 1963, and executive director of Social Security Administration from January, 1963 to March, 1967.
He was a resident of Washington, D.C. until his death there on October 10, 1991.
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