The question of whether judges’ personal characteristics and values bias their decision making has long been debated, yet far less attention has been given to how personal characteristics affect public perceptions of bias in their decision making. Even genuinely objective judges may be perceived as procedurally biased by the public. We hypothesize that membership in a religious out‐group will elicit stronger public perceptions of biased decision making. Using a survey experiment that varies a judge's religious orientation and ruling in a hypothetical Establishment Clause case, we find strong evidence that judges’ religious characteristics affect the perceived legitimacy of their decisions. Identifying a judge as an atheist (a religious out‐group) decreases trust in the court, while identifying the judge as a committed Christian has no bearing on legitimacy. These results are even stronger among respondents who report attending church more often. Thus, we argue that perceptions of bias are conditioned on judges’ in‐group/out‐group status.