What characteristics do state supreme court justices prioritize when choosing leaders? At the federal level, collegial court leaders are appointed or rotated by seniority. A plurality of states permit peer-vote selection, but the consequences of employing this mechanism are not well known. We develop a theory of chief justice selection emphasizing experience, bias, and politics. Leveraging within-contest variation and more than a half century’s worth of original contest data, we find that chief justice peer votes often default to seniority rotation. Ideological divergence from the court median, governor, and legislature is largely unassociated with selection. Justices who dissent more than their peers are, however, disadvantaged. We find no evidence of discrimination against women or people of color. The results have implications for policy debates about political leader selection.