Background <p>Nigeria accounts for 28% of global maternal deaths in 2020, with most women giving birth to children outside a health facility, especially from the northern region of the country. Non-facility births are detrimental to achieving SDG 3.1, which aims to reduce the global maternal mortality ratio to less than 70 per 100,000 live births. This study estimated the trend in non-facility births in northwestern Nigeria and identified the social determinants that were strongly influential from 2003 to 2018.</p> Methods <p>Cross-sectional data from four rounds of the Demographic and Health Survey of Nigeria (2003, 2008, 2013, 2018), with a weighted sample of 18,494 women with birth histories from the northwestern sub-region, were pooled and analysed. Binary logistic regression analysis was used to identify the social determinants of non-facility births during the period covered.</p> Results <p>Non-facility births remained persistently high, accounting for approximately 88% of births during the study period; the prevalence declined marginally from 86.7% in 2003 to 84.3% in 2018. Women’s education, religion, parity and household wealth were the most significantly influential (<i>p</i> &lt; .05) social determinants of non-facility births in the sub-region.</p> Conclusion <p>Policymakers should initiate region-specific programmes that consider the socio-cultural and economic peculiarities of the northwestern sub-region and involve key stakeholders, such as religious and traditional leaders, to promote facility-based births and reduce maternal mortality.</p>