To understand factors influencing nurse manager retention or intention to leave, develop a preliminary theoretical model and identify strategies and interventions for workforce planning. Systematic review update of literature with integrated design of mixed research synthesis. We included peer-reviewed articles examining factors influencing retention or intention to leave for front-line, middle or patient care nurse managers. Authors independently screened articles for inclusion and assessed included articles for quality. We adhered to a convergent synthesis approach. Nine databases included MEDLINE, EMBASE, PsychINFO, CINAHL Plus with Full Text, ERIC, Health Source Nursing/Academic Edition, Scopus, ProQuest Dissertations and Theses and LILACS in January 2023. Thirty-five studies published between 1990 and 2022, 22 quantitative and 13 qualitative or mixed methods, were included. 155 factors influencing nurse manager retention, intention to stay, or turnover were reported. Job satisfaction was most frequently examined (n = 7), followed by factors such as empowerment (n = 3), decision-making (n = 3) and resilience (n = 2). We developed a preliminary theoretical model demonstrating staff relations and leadership, organizational and job characteristics, socio-demographics, personal characteristics, well-being and nurse manager relationship with work influence managers' intention to stay or to leave. Nurse managers who were empowered, satisfied with their work, received constructive feedback and found meaning in their roles showed greater intent to stay. Nurse administrators can ensure managers are provided with authority to make decisions that promote autonomy. Work cultures that allow for regular meaningful constructive feedback from staff and leaders may contribute to nurse managers feeling valued. Understanding factors that influence job retention or intention to leave may help nurse managers and their supervisors identify areas for strategy and intervention design to ensure sustainability of this workforce. PRISMA 2020 Guidelines. No patient or public contribution.