Studies have revealed that well formulated strategy, efficient and effective strategy implementation has significant influence on organization’s success leading to sustainability, wherein, an absence of sufficient implementation process hinders organization’s success. Yet little research if any has been done in religious congregations and none had been carried out in the Institute of Sister Ministers of the Infirm (MI) which has been in existence in Kenya since 1976. In this study, we empirically examined the extent of strategic plan implementation success in the years 2014-2017 in the Institute of MI. Secondly, the study investigated the critical factors influencing the implementation of the strategic plan. It was guided by two theories, namely: Resource Based View Theory (RBVT) and Upper Echelons Theory (UET). A case study research design was adopted and employed a mixed method approach skewing towards description in generating and analyzing data. The data was collected through questionnaires, individual interviews, and documents of MI. In-depth interviews and surveys were drawn from 28 Sister Ministers of the Infirm in Kenya. The findings revealed that the implementation of the strategic plan was significantly effective. In addition, 3 key success factors that influenced the implementation process were identified, namely: Human capital with greatest influence of 96.4%, Effective leadership, and lastly financial resources. It was concluded that the above factors had significant impact on the strategy implementation process. The study recommends the top leadership of Institute of the Infirm to be more effective, and to renew the strategic plan as it moves towards the Institutes’ sustainability; in addition, to invest in the local available resources for an efficient, effective and full implementation of strategies in its efforts towards sustainability. The researchers recommend another study to be carried out in more than one religious Congregation for the sake of valid generalization of findings and significant contribution to theory building.

Key Words: Sister Ministers of the Infirm (MI), Strategy Implementation, Effective Leadership, Sustainability, Human Capital & Financial resources