Purpose The purpose of this paper is to examine the effects of servant leadership on employees' promotive voice behavior and prohibitive voice behavior by focusing on the mediating role of job engagement and the moderating role of proactive personality. Design/methodology/approach Time-lagged data were collected using a field survey research design. The participants included 216 employees and 23 supervisors in two commercial banks in China. Findings Perceived servant leadership was positively related to employees' promotive and prohibitive voice behavior, and these relationships were mediated by enhanced job engagement. In addition, employees' proactive personality amplified the relationship between perceived servant leadership and job engagement, and the mediating effect of job engagement on the relationship between perceived servant leadership and voice behavior. Research limitations/implications This study enhances understanding of the mechanisms underlying the servant leadership - voice model by identifying the mediating role of job engagement. The results also demonstrate the moderating role of proactive personality in enhancing the effects of servant leadership. However, the survey design was not longitudinal, which limits the study's ability to confirm causality. Practical implications The findings reveal that servant leadership, employees' job engagement, and proactive personality can facilitate employees' promotive and prohibitive voice behavior. Originality/value This study addresses the unexplored mediating mechanism of the relationship between servant leadership and voice behavior, and offers new directions for servant leadership and voice research.