James Stewart (Jefferson Smith)Jean Arthur (Saunders)Claude Rains (Senator Joseph Paine)Edward Arnold (Jim Taylor)Guy Kibbee (Governor Hopper)Thomas Mitchell (Diz Moore)Eugene Pallette (Chick McGann)Beulah Bondi (Ma Smith)H.B. Warner (Senate Majority Leader)Harry Carey (President of the Senate)Astrid Allwyn (Susan Paine)Ruth Donnelly (Mrs. Hopper)Grant Mitchell (Senator MacPherson)Porter Hall (Senator Monroe)H.V. Kaltenborn (H.V. Kaltenborn)Charles Lane (Nosey)Pierre Watkin (Senate Minority Leader)Dick Elliott (Carl Cook)
A naive youth leader is appointed to fill a vacancy in the U.S. Senate. His idealistic plans promptly collide with corruption at home and subterfuge from his hero in Washington, but he tries to forge ahead despite attacks on his character.