Background Adverse obstetric outcomes have been commonly associated with early childbearing in many low-and middle-income countries. Despite this evidence, scholarly information on early childbearing in the sub-Saharan African region, especially Nigeria, is limited. This study examines the predictors of young maternal age at first birth among women of reproductive age in Nigeria using multi-level analysis. Methods Data from the most recent Nigeria Demographic and Health Survey conducted in 2018 were analyzed. A total of 29,949 women of reproductive age (15–49 years) were considered for the study. Descriptive statistics using weighted percentage and chi-square test of independence (χ²) were first used to describe the variables of interest. This procedure was followed by a multilevel analysis of factors associated with young maternal age at first birth in Nigeria at p<0.05 level of significance. Results Approximately 36.80% of the sample population had their first birth before the age of 18. Mothers residing in the North-East region [aOR = 1.26; 95% (CI = 1.13–1.42)] and practicing Islam [aOR = 1.17; 95% (CI = 1.05–1.29] were more likely to have their first birth before the age of 18 than those in the North-Central region and those practicing Christianity. Living in communities with medium literacy level [aOR = 0.90; 95% (CI = 0.82–0.99)] and high literacy level [aOR = 0.71; 95% (CI = 0.62–0.81)], being within richest wealth index [aOR = 0.61; 95% (CI = 0.53–0.71)] and being Yoruba [aOR = 0.46; 95% (CI = 0.39–0.56)] were associated with lower odds of young maternal age at first birth. Conclusion More than one-third of women of reproductive age in Nigeria had given birth to their first child before 18 years. Thus, there is a need for the Nigerian government and other stakeholders, including Non-Governmental Organisations and Civil Society Organisations to formulate and implement policy interventions targeted at reducing early childbearing among women of reproductive age in Nigeria.