This study critically examines the effect of energy poverty on health and education outcomes for 50 developing countries in the period 1990–2017. We construct an aggregate energy development index and empirically test if the effect on development outcomes is conditioned by thresholds determined by the degree of poverty and income per capita. Our empirical results show that lower energy poverty is associated with higher health and education outcomes. However, we find that access to electricity has a more substantial positive effect on development outcomes than energy use. The threshold regression estimates show that there is a greater effect of energy development index on life expectancy rates where the poverty headcount ratio is high. Conversely, energy development index has a greater effect on infant mortality rates where the poverty headcount ratio is low, or income per capita is high. We do not find a threshold effect of poverty and income per capita in the education sector. These findings have strong policy implications for developing countries, showing that a lack of access to electricity remains a critical obstacle for achieving greater economic development, and poverty plays a crucial role in shaping these countries' health outcomes.