He defeated the anti-Long incumbent, former Republican Henry E. Hardtner of La Salle Parish.

In the litigation that reached the Louisiana Supreme Court, it ruled that holding both legislative and executive positions simultaneously was unconstitutional.

Allen was elected governor in the shadow of Huey Long, who had resigned after being elected as US Senator from Louisiana and relocated to Washington, D.C.. Allen was considered a political stooge for former governor Long.

One week before his death, he won the Democratic nomination in the special election to fill the vacancy in the U.S. Senate caused by Huey Long's assassination.

K. Allen Bridge, which carries U.S. 190 (Airline Highway) across the Mississippi River in Baton Rouge, as well as the Long-Allen Bridge over the Red River between Shreveport and Bossier City, among others.