A stronger understanding of the factors influencing implementation of interventions in community-based early childcare settings is needed. The purpose of this systematic review was to synthesize existing research on facilitators and barriers to implementation and sustainability of nutrition and physical activity interventions in early childcare settings targeting 2–5-year-old children, including considerations for equitable implementation. This review adhered to PRISMA 2020 guidelines. Peer-reviewed literature was searched in PubMed, EMBASE, CINAHL, ERIC, and PsycINFO databases up to September 2020. Primary research studies that examined facilitators and barriers (or related synonyms) to the implementation and sustainability of nutrition and physical activity interventions in early childcare settings were eligible for inclusion. The search yielded 8092 records that were screened by four analysts in Covidence software with a final review of 24 studies. Two independent reviewers conducted study selection, data extraction, and quality appraisal (Mixed Methods Appraisal Tool). A “best fit” framework was applied using the Consolidated Framework for Implementation Research (CFIR) constructs to code barriers and facilitators. The most salient constructs were (1) “Available Resources,” which was composed of time, staffing, space, and staff trainings; (2) adaptability; and (3) compatibility, the latter two indicating that easily modifiable interventions facilitated a smoother “fit” and were more likely to be successful, given adequate site-level resources. Only nine (28%) reported the use of a theory, model, or framework to guide evaluation; six studies (24%) included factors related to sustainability; and nine studies (38%) conducted their interventions with low-income or minoritized groups. The findings point to the need for intervention evaluations examining nutrition and physical activity to more consistently consider (a) sustainability factors early on in design and adoption phases; (b) use of theory, model, or framework to guide evaluation; and (c) equity-related frameworks and considerations for how equitable implementation. (author abstract)