Health improvement is a crucial determinant of economic growth; however, the impact of health on economic growth is affected by the level of poverty in any nation. Previous studies have focused more on the health–growth nexus, but the role of poverty reduction and the threshold of health required to mitigate the effect of poverty on economic growth were missing. This paper, therefore, examined the life expectancy–growth nexus and the role of poverty reduction with the view to determine the contribution of health to growth and poverty reduction and the threshold of health required to mitigate the adverse effect of poverty on economic growth in Nigeria. Based on the endogenous growth theoretical approach, the link between life expectancy, poverty incidence, and economic growth was estimated using the fully modified ordinary least square method. Findings showed that health contributes positively to economic growth and also mitigates the adverse effect of poverty on economic growth in Nigeria. The study determined the minimum threshold of life expectancy of 64.4 years as a health improvement annual benchmark. Therefore, for Nigeria to achieve sustainable economic growth and significant poverty reduction, policies aimed at achieving the newly determined health improvement threshold from the current annual average of 47.8 years are fundamental.