The study aimed to determine the influence of institutional factors on the mainstreaming of Nature-Based Solutions (NBS) into Local Development Plans and the actual implementation of NBS projects for climate change adaptation and mitigation in Zambia’s municipalities, using Mumbwa Town Council as a case study. A comprehensive review of literature on climate change adaptation, mitigation, resilience building, NBS mainstreaming, implementation, and institutional factors was conducted. Qualitative methods were employed for data collection and analysis, utilizing semi-structured interview guides to gather primary data from key informants and document reviews to collect secondary data. Data analysis was performed using Atlas.ti in which co-occurrence analyses were conducted to determine the relationship between the various institutional factors and the NBS mainstreamed and implemented. The research findings indicate that Mumbwa has successfully integrated NBS into its local development plans across five main categories: sustainable forest management, water ecosystem conservation, conservation agriculture, wildlife ecosystem restoration, and urban greening, all of which have been implemented through various projects. The study identifies several institutional factors that have facilitated the mainstreaming and implementation of NBS, including institutionalization, supportive local and national policies, a holistic, flexible, and inclusive planning system, good governance, and international funding. The study concludes that to a high extent, these facilitating factors have had a positive influence on NBS mainstreaming and implementation in Zambia, outweighing the hindering factors.