This study investigates health intervention intensity in Nigeria and its implications for maternal mortality, infant mortality and life expectancy. Existing studies have largely focused on the direct relationship between health expenditure and health outcomes without considering health intervention intensity as a single variable to measure government, private and foreign/donor health interventions. The main objective of this study is to determine the causal relationship between health intervention intensity, maternal mortality, infant mortality and life expectancy in Nigeria for the period 1990 to 2024. Data on health intervention intensity is obtained using a weighted composite index which is standardized to fall between 0 and 1. The study adopts a quantitative research design based on secondary time-series data sourced from World Bank Development Indicators, Central Bank of Nigeria Statistical Bulletin and World Health Organization, as well as relevant donor health financing databases. Toda-Yamamoto causality approach is used to examine the direction of causality among variables. The results indicate that health intervention intensity has significant causal relationship with maternal mortality and life expectancy in Nigeria, but not infant mortality. The conclusion is that although health interventions in Nigeria are effective in enhancing long-term survival and maternal outcomes, their effect on infant health is minimal, perhaps because of inefficiencies in neonatal care delivery or slow effects of interventions. The study recommends coordinated financing strategy across public, private and donor sources, strengthening of neonatal and child health systems, and sustaining and expansion of integrated health investments across public, private and donor-supported programmes.