The chief characters in the central action of the novel are the trio of ambitious young people seeking success and identity in the world dominated by Bogan Murdock's interests. These three, along with Windham, the hill-country murderer turned evangelist, and his polar opposite, the ruthless pragmatist, Bogan Murdock, are the central characters—even though Murdock is presented primarily through the point of view of others and through the impact of his actions.

Of these three young people, the most interesting may be Sue Murdock, whom Warren portrays as a rebellious woman ahead of her time, seeking emancipation from conventional roles. Unfortunately, Sue, who also represents the modern spirit in quest of values or a soul, is destroyed by her search, because she unwisely becomes the lover of Slim Sarrett. Although Sue learns the weaknesses and flaws of Sarrett and Jerry Calhoun, the former football player trying to climb the ladder of success, her flight from her life as Bogan Murdock's spoiled daughter is a frustrated effort. It is true that she finds a certain stability in her relationship with Jason Sweetwater, an idealist with conviction; but their differences also destroy their relationship. At the end of her unhappy life, when she is strangled by the vengeful Sarrett, Sue seems to have become a passive and willing victim, who offers a curious complicity in her murder.

The two young male protagonists are less tragic, and perhaps not as interesting. Sarrett's air of studied indifference and literary ambition manage to trick readers, as well as Sue Murdock. However, once his deception and malice become known, he often seems to be a caricature of literary opportunism, merely an ambitious teaching assistant and failed poet whose interest in Sue was partially motivated by his attraction to her father's influence. Perhaps Sarrett was a character whose nature changed in the process of Warren's writing. At any rate, Warren missed the opportunity to make Sarrett a memorable portrait of jealousy and malice.

By contrast, Jerry Calhoun, whose ambition is at first merely to become another American success story modeled on that of Bogan Murdock, becomes a more interesting character when his moral nature is tested. As a remorseful puppet of Bogan Murdock, desiring to confess the truth and regain something of his integrity, Calhoun becomes a more sympathetic character. His final sequence of self-exploration, in which he faces the reality that he had sought to repudiate his father, is a powerful and impressive passage.

Unlike these three, Windham, the hillcountry "born-again" preacher, is something of an outsider, although his statement reveals much of the truth about Bogan Murdock. Windham's compulsion to atone for his crime and his unconditional commitment to his brand of fundamentalist Christianity offers a strong contrast to the more intellectual and ambitious trio of young protagonists. Warren's use of mountaineer dialect and idiom in Windham's narrative is impressive, and Windham's narrative often seems to gain in vividness and authenticity because of the language he uses.

There is a sense in which Bogan Murdock is a major character, yet he is "on stage" only occasionally in the novel. One learns of Murdock's character through its impact on others. Murdock's private self is not revealed, perhaps because Warren intends to show that Murdock, like Willie Stark in All the King's Men, sacrifices his private life to his unending quest for power. Most of the time, Murdock is depicted as a man trying to live up to a self-conceived image of power and authority, as in the novel's final scene in which Murdock seems to be justifying his actions, rather than showing that he has learned from the tragedy he has created.

Aside from its strong major characters, the lesser characters in At Heaven's Gate are also lively and memorable. Duckfoot Blake, Jerry's fellow employee, adds a note of amusing and colorful cynicism. Private Porsum, based on the actual Sergeant Alvin York (whom Warren interviewed), is essentially a minor figure drawn into Murdock's chicanery; but his moment of soul searching is vividly rendered, as is also his memory of his moment of heroism in France. Jason Sweetwater, Sue's third lover, is a believable labor activist, a man of strong will and determination who might have stolen the book if Warren had given him more space.

Finally, Jerry Calhoun's father and Uncle Lew are impressive minor characters. The long suffering Mr. Calhoun is a kind and forgiving farmer, who accepts Jerry's mistakes. Mr. Calhoun's foil is his cynical brother, Jerry's Uncle Lew, who voices the world's sarcasm about Jerry and others who seek higher attainments. Although Lew seems to be correct in his assessment of Jerry, the father asserts his authority and unconditional love for his son in his final scene, when Mr. Calhoun will not allow Lew to wake Jerry from a deep morning sleep, after Jerry's bitter ordeal in jail. Both characters, the father and Lew, are memorably drawn.