The film depicts the events surrounding the Johnson's impeachment, and "presents its title character as Lincoln’s worthy successor who runs afoul of vindictive Radical Republicans.

"[2] Like most U.S. historical films made during World War II, Tennessee Johnson has a strong underlying theme of national unity.

In a climactic but fictional scene, he delivers an impassioned speech to the senators sitting in judgment of him, and warns them that failure to readmit the former Confederate states will leave America defenseless before its overseas foes.

He barters his services to the librarian, Eliza McCardle (Ruth Hussey), in return for her teaching him to read and write, and eventually marries her.

Abraham Lincoln chooses him for his vice president in part because they share similar views on reconciling with the South after the war is won, unlike powerful, vengeful Congressman Thaddeus Stevens (Lionel Barrymore).

Vincent Price, Mostel and Ben Hecht, among others, petitioned the Office of War Information to destroy the film in the interest of national unity.

Kauffman surmised that Manny Farber had written the most intelligent opinion on the matterThe New Republic when he said: "Censorship is a disgrace, whether done by the Hays office and pressure groups, or by liberals and the OWI.