Background: Research to date has focused on strategies and resources used by effective champions of healthcare change efforts, rather than personal characteristics that contribute to their success. We sought to identify and describe champion attributes influencing outcomes of healthcare change efforts. To examine attributes of champions, we used postpartum contraceptive care as a case study, because recommended services are largely unavailable, and implementation requires significant effort. Methods: We conducted a comparative case study of the implementation of inpatient postpartum contraceptive care at 11 U.S. maternity hospitals in 2017-18. We conducted site visits that included semi-structured key informant interviews informed by the Consolidated Framework for Implementation Research (CFIR). Phase one analysis (qualitative content analysis using a priori CFIR codes and cross-case synthesis) showed that implementation leaders ("champions") strongly influenced outcomes across sites. To understand champion effects, phase two inductive analysis included (1) identifying and elaborating key attributes of champions; (2) rating the presence or absence of each attribute in champions; and 3) cross-case synthesis to identify patterns among attributes, context, and implementation outcomes. Results: We completed semi-structured interviews with 78 clinicians, nurses, residents, pharmacy and revenue cycle staff, and hospital administrators. All identified champions were obstetrician-gynecologists. Six key attributes of champions emerged: influence, ownership, physical presence at the point of change, persuasiveness, grit, and participative leadership style. These attributes promoted success by enabling champions to overcome institutional siloing, build and leverage professional networks, create tension for change, cultivate a positive learning climate, optimize compatibility with existing workflow, and engage key stakeholders. Not all champion attributes were required for success, and having all attributes did not guarantee success. Conclusions: Effective champions appear to leverage six key attributes to facilitate healthcare change efforts. Prospective evaluations of the interactions among champion attributes, context, and outcomes may further elucidate how champions exert their effects.