Billy Budd is the story of the titular seaman's trial and execution after he strikes and accidentally kills an officer aboard the HMS Bellipotent, a British warship. Captain Vere, his commanding officer, deliberates on points of law and martial discipline weighed against Budd's pure character. The conclusion of the novel offers varying perspectives on Budd's personality and reputation, showing an elegiac account by fellow seamen, a naval denouncement, and a report of Vere's death and apparent regret for his actions.
The plot follows Billy Budd, a seaman impressed into service aboard HMS Bellipotent in the year 1797, when the British Royal Navy was reeling from two major mutinies and was threatened by the Revolutionary French Republic's military ambitions. He is impressed from another ship, The Rights of Man (named after the book by Thomas Paine). As his former ship moves off, Budd shouts, "Good-bye to you too, old Rights-of-Man ."
Billy, a foundling, has an openness and natural charisma that makes him popular with the crew. He arouses the antagonism of the ship's master-at-arms John Claggart. Claggart, while not unattractive, seemed somehow "defective or abnormal in the constitution," possessing a "natural depravity." Envy was Claggart's explicitly stated emotion toward Budd, foremost because of his "significant personal beauty," and also for his innocence and general popularity. (Melville further opines envy is "universally felt to be more shameful than even felonious crime.") This leads Claggart to falsely charge Billy with conspiracy to mutiny. When the captain, Edward Fairfax "Starry" Vere, is presented with Claggart's charges, he summons Claggart and Billy to his cabin for a private meeting. Claggart makes his case and Billy, astounded, is unable to respond, due to a stutter which grows more severe with intense emotion. He strikes his accuser to the forehead, and the blow is fatal.
Vere convenes a drumhead court-martial. He acts as convening authority, prosecutor, defense counsel and sole witness (except for Billy). He intervenes in the deliberations of the court-martial panel to persuade them to convict Billy, despite their and his beliefs in Billy's moral innocence. (Vere says in the moments following Claggart's death, "Struck dead by an angel of God! Yet the angel must hang!") Vere claims to be following the letter of the Mutiny Act and the Articles of War.
Although Vere and the other officers do not believe Claggart's charge of conspiracy and think Billy justified in his response, they find that their own opinions matter little. The martial law in effect states that during wartime the blow itself, fatal or not, is a capital crime. The court-martial convicts Billy following Vere's argument that any appearance of weakness in the officers and failure to enforce discipline could stir more mutiny throughout the British fleet. Condemned to be hanged the morning after his attack on Claggart, Billy before his execution says, "God bless Captain Vere!" His words were repeated by the gathered crew in a "resonant and sympathetic echo."
The novel closes with three chapters that present ambiguity: