- Groucho Marx as Rufus T. Firefly, the leader of Freedonia
- Harpo Marx as Pinky, a spy for Sylvania
- Chico Marx as Chicolini, another spy for Sylvania
- Zeppo Marx as Lt. Bob Roland, Firefly's secretary
- Margaret Dumont as Mrs. Gloria Teasdale, a rich widow who underwrites the budget of Freedonia
- Louis Calhern as Ambassador Trentino of Sylvania, who schemes to have his country annex Freedonia
- Raquel Torres as Vera Marcal, a femme fatale spying for Sylvania
- Edgar Kennedy as the blustery lemonade vendor
- Edmund Breese as Former President Zander, Firefly's predecessor
- Edwin Maxwell as the Secretary of War
- William Worthington as First Minister of Finance
- Davison Clark as Second Minister of Finance
- Charles Middleton as prosecutor
- Leonid Kinskey as Trentino's Sylvanian "agitator"
- Verna Hillie as Trentino's secretary
- George MacQuarrie as first judge
- Fred Sullivan as second judge
- Eric Mayne as third judge
- Wade Boteler as officer at battle headquarters (uncredited)
- Carrie Daumery as reception guest (uncredited)
Cast notes
Comparing the original scripts with the finished film, most of the characters' initial scripted names were later changed. Only the names of Chicolini and Mrs. Teasdale were kept. Groucho's character—originally named "Rufus T. Firestone"—eventually became Rufus T. Firefly, while the name of Harpo's character—named Pinky in the final product—was given in the Paramount pressbook as "Brownie".[10] "Ambassador Frankenstein of Amnesia" was quickly changed to Ambassador Trentino of Sylvania. Zeppo's character remained Firefly's son until very late in production, finally becoming Bob Roland, his secretary; also, Mrs. Teasdale's niece "June Parker" transformed into Vera Marcal, first introduced as Trentino's "niece" before ultimately becoming his companion.[11]
