Zambia's energy sector is heavily reliant on hydropower, which accounts for over 83% of its 3,800 MW installed capacity as of December 2023. This dependency, coupled with the impacts of climate change, has led to increasing energy insecurity, particularly during frequent droughts, which disrupt electricity supply. Additionally, the country faces significant challenges in extending electricity access, especially in rural areas where the average access rate is only 8%. In response, the Zambian government has set ambitious targets to diversify the energy mix to achieve 30% electricity production from variable renewable sources. To support Energy Transition Pathways for Zambia and sustainable development , study employed the Advanced Energy System Modelling Using OseMOSYS an Open-Source Energy Modelling System to explore three energy transition scenarios: Business-As-Usual (BAU), Government Renewable Energy Policy (REW), and Drought Impact Scenario (DIS). The scenarios assess the integration of renewable energy, technological advancements, and policy interventions up to 2070. The results highlight the critical need for diversification in Zambia's energy mix. The REW scenario, which emphasizes renewable energy integration, shows significant potential for reducing greenhouse from about 2000 ktCO2 to about 1600 ktCO2 and stabilizing investment costs. The DIS scenario underscores the importance of resilience strategies in mitigating the impacts of droughts on the hydropower-dependent energy system. Overall, this study provides essential insights and policy recommendations for guiding Zambia's transition towards a more sustainable and resilient energy future.