Capacity building may play an important role in improving classroom teachers' and early childhood educators' (ECE) capacity to implement physical activity and FMS interventions. Capacity building is the development of knowledge, skills, and structures to improve the capability of individuals and organisations to achieve effective health promotion. This review aimed to determine the efficacy of capacity building interventions on teachers' and ECEs' perceived capabilities, knowledge, and attitudes relating to physical activity and fundamental movement skills. An exhaustive literature search of six electronic databases was conducted. Controlled, single-group pre-post studies were included if they measured the effect of a capacity building intervention on in-service or pre-service classroom teachers' (primary or secondary) or ECEs' physical activity or fundamental skills related perceived capabilities, knowledge, or attitudes. The effects of interventions were synthesised using random effects meta-analysis. Subgroup analysis and meta-regression was conducted to determine if the effects differed based on study design, type of teacher (ECE vs. primary school), or teacher level (pre-service vs. in-service). A total of 22 studies reporting on 25 unique samples were included in the meta-analyses. Only studies reporting on ECEs and primary school teachers were identified. Interventions most commonly included training/professional development, resources and toolkits, communities of practice, mentorships, and ongoing support. Results showed that capacity building interventions significantly improved teachers' and ECEs' perceived capabilities (g = 0.614, 95% CI = 0.442, 0.786), knowledge (g = 0.792 95% CI = 0.459, 1.125), and attitudes (g = 0.376 95% CI = 0.181, 0.571). The effects did not differ significantly as a function of any of the moderators examined. Findings from this review provide strong support that capacity building interventions are efficacious at improving teachers' and ECEs' perceived capabilities, knowledge, and attitudes related to promoting physical activity and teaching fundamental movement skills. Pre-service teachers and ECEs should be provided training in physical activity and fundamental movement skills as part of their degrees, and continual professional development and capacity building should be offered to in-service teachers and ECEs to promote physical activity and fundamental movement skills in children.