All the King's Men is long and complex and Jack indulges in long digressions, which means, at times, the book briefly enters into a variety of genre categories. The story becomes a romance while Jack describes his love affair with Anne, a mystery as Jack seeks out the Irwin scandal, and a thriller as the novel reaches its climax in violent gunshots.
But despite the fact that Robert Penn Warren wrote that All the King's Men was "never intended to be a book about politics," the novel is, undoubtedly and predominantly, political fiction. The genre of "political fiction" is more specific than that of the "social novel," which addresses political ideas through narrative. "Political fiction" describes novels that depict politicians and their political affairs in an attempt to describe deeper moral truths. (Social novels do the opposite, using stories about deeper moral truths in an attempt to describe politics.) All the King's Men follows a tradition of nineteenth-century novels on political affairs, including Benjamin Disraeli's historical novels about new English politicians and Turgenev's Fathers and Sons. Later novels of this genre in American history include Gore Vidal's novels about Lincoln, John Adams's opera Nixon in China, and even the more modern Lincoln in the Bardo. In all these novels, as in All the King's Men, political actions form much of the plot. The narrative energy in Warren's novel comes from the tension between Willie's strong sense of morality and his ambitions as governor. In other words, politics is at the center of the plot, making All the King's Men political fiction.
The novel can also be described as American realism, though it was published a few decades after the peak of that literary genre. Realism, in American literature, refers to a movement in the late nineteenth century which included novels which sought to depict life as it was truly lived across social divisions. Realist novels also typically had plots concerning powerful men who come to tragic ends because of their boundless ambition. In this way, Warren's most direct literary ancestor might be William Dean Howells, author of The Rise of Silas Lapham, which depicts a similar rags-to-riches story, followed by an untimely end, as that of Willie Stark. All the King's Men, with its tragic, ambitious protagonist and honest depiction of life in Louisiana, is a realist novel as well as a political one.