On his first appearance, Willoughby appears to be the romantic hero of the novel as he rescues Marianne and carries her home. "Uncommonly handsome," he has a charming voice and gallant manners. Sir John describes him as "As good a kind of fellow as ever lived. . . . A decent shot . . . there is not a bolder rider in England."
Attracted to Marianne, he pays her great attention. Something of his real nature shows when he makes malicious fun of Marianne's admirer, Colonel Brandon. As time goes on, he is seen to have no strength of purpose; he leaves Marianne without explanation when Mrs. Smith discovers that he has seduced Colonel Brandon's protégé, Eliza Williams.
He avoids Marianne until she begs him to speak to her at a dance. Later he sends her a cruel and curt letter, saying that he had never been seriously attracted to her. After marrying Miss Grey, a wealthy woman who makes him unhappy, he repents of his behavior to Marianne. When Sir John tells him of her serious illness, he travels to Cleveland at once to find out how she is. He tells Elinor that his fiancée dictated the letter to Marianne and made him send it.
He convinces Elinor of his repentance. During their talk, "Her thoughts were silently fixed on the irreparable injury which too early an independence and its consequent habits of idleness, dissipation, and luxury, had made in the mind, the character, the happiness, of a man who, to every advantage of person and talents, united a disposition naturally open and honest, and . . . [an] affectionate temper."