Martin Eden is the protagonist, a writer with anti-socialist principles and a strongly individualist worldview. He works hard to achieve his ambitions and seeks to win the hand of Ruth Morse.

He starts out as a sailor but slowly grows in book-learning, combining intellect with practical knowledge of the world. As the novel progresses, he becomes disenchanted with the bourgeois class and its values. He embraces extreme individualism and the idea of the "superman," while rejecting both capitalism and socialism. However, his extreme view leads to his eventual suicide.

Ruth Morse is from the bourgeois class and the apple of the eye of the working-class hero. Ruth falls for Martin; however, she refuses to be his wife without the consent of her parents, who find Martin's finances and social status wanting. While Ruth and her world initially appear ideal to Martin, he comes to see their lifestyle as a shallow sham. Ruth is revealed to be a snobby, cold woman and she rejects Martin when he can't make good fast enough.

Lizzie Connolly is an Irish-American worker who loves Martin. Her affections remain unrequited, but Martin appreciates how she loves him for who he is, sans money and prestige. Despite coming to realize the unworthiness of the snobby Ruth after she rejects him in a letter, Martin never settles down with Lizzie, since the class gulf between them is too great.

Russ Brissenden is a socialist poet who engages in political dialogue with Martin. However, he is not a well man and eventually commits suicide. Ironically, his book of poetry is published to great success just after his death.