This study examines Nigeria's energy system transformation from 2025 to 2060 using the LEAP (Low Emissions Analysis Platform) model. Unlike many analyses that base projections solely on fixed capacity expansion targets, it integrates both a proposed expansion plan and demand-driven capacity growth to align electricity generation with multi-sector energy use, population growth, and economic development. Three scenarios were evaluated: a Business as Usual (BAU) trajectory, a Gas Transition Economy (GTE), and an Ambitious Green Transition (AGT). The BAU scenario has the highest total emissions by 2060, at 783.4 MtCO₂e, followed by GTE at 766.1 MtCO₂e. In contrast, the AGT scenario, driven by large-scale electrification and renewable energy, presents the most sustainable pathway, reducing total emissions to 493.5 MtCO₂e. Notably, the AGT pathway also delivers the greatest developmental benefits. Despite having the lowest final energy demand (3991.4 PJ), it achieves the highest per capita electricity access, reaching 2.86 kWh/day by 2060. This is a direct result of strategic electrification and efficiency gains that decouple human development from raw energy consumption. A key conclusion of this study is that Nigeria's path to a low-carbon, inclusive future lies in prioritizing strategic electrification and aggressive renewable energy targets, which are proven to reduce emissions while simultaneously improving energy access for its citizens.