This paper studies the effect of punishment severity on jury decision-making using a large archival data set from the Old Bailey Criminal Court in London from 1715 to 1900. We take advantage of two natural experiments in English history, which result in sharp decreases in punishment severity: the offense specific abolition of capital punishment in the 1800s and the temporary and unexpected halt of penal transportation during the American Revolution. Using a difference-in-differences design to study the former and a pre-post design to study the latter, we find that decreasing expected punishment (especially via the end of the death penalty), had a large, significant and permanent impact on jury behavior, generally leading to the jury being ‘harsher’. Moreover, we find that the size of the effect differs with defendants’ gender and criminal history. These results raise concerns about the impartiality of juries as well as the implicit assumption often made when designing and evaluating criminal justice policies today – that the chance of conviction is independent of the harshness of the penalty.