The play opens in a jury room in New York City, 1957, which will be the setting for the entire action of the play. A judge speaks off-stage, telling the jurors that they must now begin their deliberations. Their verdict concerns a first-degree murder charge. The accused is a young boy suspected of murdering his father. As the judge emphasizes, a verdict of “guilty” will result in a mandatory death sentence for the accused.

The 12 jurors then enter the room. It takes a while for the deliberations to begin, as the jurors continue chatting amongst themselves or seek refreshment. During this time, several jurors express impatience, while others appear quiet and withdrawn. When the deliberations begin, the 1st Juror/Foreman calls a preliminary vote: There are 11 votes for “guilty” and only 1 vote for “not guilty.” The “not guilty” vote belongs to the 8th Juror, whose dissent astonishes the others. The 8th Juror explains his vote by saying, “There were eleven votes for ‘guilty.’ It’s not easy for me to raise my hand and send a boy off to die without talking about it first” (Act I, 22). The 8th Juror asks for an hour of deliberations; the other jurors agree.