Background <p>The proactive service behavior of employees in the public sector has important effects on the public’s perceptions of service quality. However, it has rarely been studied among public sector employees. As job design research has developed, the social and relational aspects of work have been neglected. On the bases of person‒job fit theory and the proactive motivation model, this study explores the influences and mechanisms of two dimensions of relational job characteristics—job impact on service recipients and job contact with service recipients—on Chinese public sector employees’ proactive service behavior. Specifically, it examines the mediating role of work calling. In addition, it explores public service motivation as a moderator of the relationships between relational job characteristics and work calling.</p> Methods <p>This study adopted a cross-sectional survey design. 342 questionnaires were collected using the paid sampling service of the <i>Questionnaire Star</i>, of which 330 (96.49%) were valid. The participants’ relational job characteristics, public service motivation, work calling, and proactive service behavior were measured. <i>SPSS</i> was used for descriptive statistical analysis and correlation analysis. Path analysis with observable variables was conducted to test the hypotheses using <i>Mplus</i>.</p> Results <p>The results indicated that job impact and job contact were positively associated with public sector employees’ proactive service behavior (<i>B1</i> = 0.099, <i>p</i> &lt; 0.01; <i>B2</i> = 0.081, <i>p</i> &lt; 0.01) and that work calling mediated the effects of job impact and job contact on proactive service behavior (<i>B1</i> = 0.032, <i>p</i> &lt; 0.05; <i>B2</i> = 0.038, <i>p</i> &lt; 0.01). Public service motivation moderated the relationship between job impact and work calling (<i>B</i> = 0.091, <i>p</i> &lt; 0.05) and the mediating effect of work calling between job impact and proactive service behavior.</p> Conclusions <p>Our findings highlight that relational job characteristics and work calling are key antecedents of proactive service behavior, with public service motivation amplifying the positive effects of job impact. In practice, these findings demonstrate that public sector organizations can improve employees’ proactive service behavior through optimizing job design to reinforce relational elements and nurturing work calling and PSM via recruitment, training, and supportive organizational settings. These strategies collectively contribute to building a more efficient and citizen-centric service-oriented government.</p>