In the play, Juror Ten exhibits intense prejudice against individuals from slum areas. Early in act 1, he declares, "You can't believe a word they say." Notably, he uses "they" to refer to the entire group rather than "he" to single out the defendant, demonstrating his inability to judge individual guilt fairly. Juror Nine, an elderly man with extensive life experience, immediately recognizes this bias and confronts Juror Ten by asking, "Since when is dishonesty a group characteristic?" Despite this, Juror Ten’s bigotry continues to fester and ultimately explodes into a lengthy speech near the end, prompting the other jurors to dismiss him. The play clearly conveys that such irrational prejudice is incompatible with the pursuit of justice. Juror Four also displays similar prejudice, although he expresses it in more socially acceptable terms: "The children who come out of slum backgrounds are potential menaces to society."

The defendant in the play hails from a slum, but there is no indication that he is not white, like all the jurors. However, in the 1957 film adaptation, the defendant is depicted in an early scene, appearing clearly Hispanic, possibly Puerto Rican. He looks sad and vulnerable, contrasting sharply with the thug-like image the jury initially imagines. This portrayal introduces a racial element to the theme of prejudice. The play ultimately delivers a positive message: prejudice is eventually overcome by reason, leaving those who express such biases to reflect on their foolishness and bigotry. Nonetheless, there's a less optimistic perspective to consider. The judicial system's ideal is for a person to be judged by a jury of peers, yet the predominantly white male jury can hardly be considered peers of the boy whose fate they decide. Furthermore, by depicting the jurors almost unanimously rejecting Juror Ten's overt racial prejudice (in a visually striking scene both onstage and onscreen), the playwright might present an overly optimistic view of 1950s American society, which was far from free of prejudice against minorities and often unwilling to confront it. Alternatively, one could argue that the playwright is conscious of these social issues and seeks to educate the audience, urging them to recognize and reject attitudes that many might unknowingly harbor.