After being urged into politics by his uncle, Judge Roscoe Tartar, Cooper ran unopposed for a seat in the Kentucky House of Representatives as a Republican in 1927. As a member of the House, he was one of only three Republicans to oppose Republican Governor Flem D. Sampson's unsuccessful attempt to politicize the state department of health; the measure failed by a single vote. Cooper supported the governor's plan to provide free textbooks for the state's school children and sponsored legislation to prohibit judges from issuing injunctions to end labor strikes, although the latter bill did not pass.