The global human population has been increasing at an alarming rate over the last 100 years and is projected by the United Nations (UN) to continue to increase and reach 10 billion by 2057, despite a declining growth rate. Although some countries and regions, primarily Japan and Europe, have stabilised or declining populations, Sub-Saharan Africa is dramatically growing at an annual rate of 2.7% as of 2019, and is projected to sustain a rapid population growth up to 2100. Addressing the subject of population growth and overpopulation is an important but unfortunately neglected task. The consequences of a large, growing human population are already having distressing impacts on the planet, both on the natural environment and on humans, especially women and children. Until recently, there have been few studies on the effects of religion and religiosity on fertility and contraceptive use, and these factors are often overlooked as possible determinants. The aim of this review is to explore and seek to clarify the role of religion and religiosity on fertility and contraceptive use in continental Sub-Saharan African countries. The review of quantitative publications supported by insights and opinions from actual quotes of respondents from qualitative studies shows that followers of African Indigenous Religions and Islam have higher fertility rates than followers of Christianity. Across Christian denominations, Catholics generally had higher fertility than Protestants although the difference is small. Followers of the Apostolic Church exhibited the highest fertility among Christian groups. Focus group discussions and in-depth interviews from the qualitative studies found that religious beliefs were frequently cited as a barrier to contraceptive uptake. The findings clearly suggest that religion influences fertility and contraceptive use, although countries differ in this respect. Few studies mentioned religiosity; existing results show a positive relationship across Sub-Saharan Africa between degree of religiosity and fertility, and a negative relationship with contraceptive use. These relationships are stronger in Islamic and Indigenous religions compared with Christianity. Religious leaders across all religions were found to be highly influential and many participants were inclined to follow the recommendations of religious leaders regarding fertility and contraceptive use. The implication of this finding is that educating religious leaders about rights-based family planning and its benefits should be part of a comprehensive strategy to increase contraceptive uptake and reduce fertility. With knowledge of its benefits, religious leaders could spread accurate messages about family planning to their followers and promote higher contraceptive use and low fertility. In addition, other important socioeconomic and cultural factors influence fertility and contraceptive use. Education, economy and access to family planning have a negative relationship with religiosity, but the strength of this relationship varies depending on religion, residence and region, with Muslims generally reported as the most disadvantaged in terms of education and wealth across Sub-Saharan Africa. Polygyny, gender attitudes, social status and misconceptions about family planning were additional influences on fertility and contraceptive use mentioned in focus group discussions and in-depth interviews from the qualitative studies. Religion and religiosity have an important role to play in relation to fertility and contraceptive use, but they also depend on other factors, their interactions and their relative influences. They have variable relationships to education, economy, gender equality, residence (rural/urban) and access to family planning, due to the different levels of these factors among and within countries in Sub-Saharan Africa. The review suggests that with a more religiously open stance towards family planning, population policies can be more easily implemented. Religion and religiosity need to be considered in surveys and studies on fertility and contraceptive use to inform and help policymakers, economic planners, program managers, researchers and survey specialists. In addition, this has the potential to improve environmental conditions in Sub-Saharan Africa.