The main characters in Elizabeth Acevedo's The Poet X include the titular character, "X" (which is the stage name that the fifteen-year-old Xiomara Batista adopted in her slam poetry group). X lives in Harlem with her family and is self-conscious about her curvy body, which elicits comments from men. She is torn between her mother's wishes that she eschew dating and men in favor of the church, and her burgeoning interest in the art of poetry.

Mami is Xiomara's mother (her full name is Altagracia Batista). She once had dreams of being a nun, and her devotion to the church leads her to compel her daughter to live a cloistered life.

Xavier Batista is Xiomara's twin brother. He is very smart and attends a different school. Xiomara calls him "Twin" and keeps his sexuality (he is gay) a secret from their mother.

Aman is a classmate of Xiomara, and she develops a crush on him. Eventually, Aman becomes Xiomara's boyfriend after they met in a science class. His family is from Trinidad, and he expresses interest in Xiomara's poetry.

Ms. Galiano is Xiomara's English teacher at school. She invites Xiomara to join the slam poetry club.