Rees studied law, was admitted to the bar in 1915, and began a law practice in Emporia. He also engaged in agricultural pursuits. Serving as a member of the Kansas House of Representatives from 1927 to 1933, he was also a member of the Kansas Senate from 1933 to 1935 and a member of the Kansas Judicial Council from 1933 to 1937. Rees was elected as a Republican to the Seventy-Fifth Congress and to the 11 succeeding Congresses (January 3, 1937 – January 3, 1961). He served as chairman of the Committee on the Post Office and Civil Service (Eightieth and Eighty-Third Congresses).