IntroductionIn the year 2019 whiles the total world under-five mortalities was estimated at about 5.2 million, Sub-Saharan Africa contributed about 55% of these global under-five mortalities. In other words, the region alone recorded about 2.8 million under-five deaths out of the global 5.2 million under-five mortalities in 2019. On the other hand, public health expenditure in Sub-Saharan Africa though very low as compared to other regions has also seen a steady increase over the years. This has resulted in an increased interest of researchers and policymakers in scrutinizing the effect of healthcare spending on health status in Sub-Saharan Africa. Thus, the purpose of this study is to investigate the association between public healthcare spending and the under-five mortality rate in low-income countries of Sub-Saharan Africa. This has become necessary due to the impact of healthcare spending on the quality and quantity of the health system and the long-run effect on health outcomes and its overall link to economic growth and development. MethodsA balanced panel of data from twenty low-income countries in Sub-Saharan Africa was sourced from the World Development Indicators dataset spanning the year 2000–2019. The under-5 mortality rate was used as the outcome variable whereas domestic health expenditure was used as the independent variable of interest. Total fertility rate, percentage population of females, the practice of open defecation, and immunization against diphtheria-pertussis-tetanus (DPT) were considered potential confounding variables. The static model was applied. To arrive at the appropriate model for the study, the robust Hausman test was employed to aid in the selection between the random effect estimator and the fixed effect estimator, and the results led to the selection of the fixed effect estimator. ResultsThe results showed that domestic health spending has a significantly negative relationship (Fixed Effects = −5.275; p < 0.05) with the under-five mortality rate in low-income countries of Sub-Saharan Africa. For every additional percentage increase in domestic health spending, it is likely to result in about 5.3 units fall in under-five mortality rate. Total fertility rate, female population, and rural people practicing open defecation were positively associated while immunization against DPTwas negatively associated (p < 0.01) with an under-5 mortality rate. ConclusionThe study revealed a strong relationship between domestic health spending and the under-five mortality rate. We conclude that a sustained increase in health expenditure and improvement in social conditions are required to reduce under-5 mortalities within low-income countries of Sub-Saharan Africa.