Abstract While the link between living in low socioeconomic status (SES) neighbourhoods and a higher risk of adverse birth outcomes has been well established, the underlying mechanisms remain poorly understood. Using the parametric g-formula, we assess the role of neighbourhood crime as potential mediator for the relationship between neighbourhood SES and birth outcomes using data on singleton births occurring in the Netherlands between 2010 and 2017 (n = 1,219,470). We estimated total and mediated effects of neighbourhood SES on small for gestational age (SGA), low birthweight (LBW), and preterm birth (PTB) via three types of crime (violent crimes, crimes against property and crimes against public order). The g-formula intervention settings correspond to a hypothetical improvement in neighbourhood SES. The hypothetical improvement in neighbourhood SES resulted in a 6.6% (95%CI=5.6,7.5) reduction in the proportion of SGA, a 9.1% (95%CI=7.6,10.6) reduction in LBW, and a 5.8% (95%CI=5.7,6.2) decrease in PTB. Neighbourhood crime jointly accounted for 28.1% and 8.6% of the total effect on SGA and LBW, respectively. For PTB, we found no evidence of mediation. The most relevant pathways were crimes against property and crimes against public order. The results indicate that neighbourhood crime mediates a meaningful share of the relationship between neighbourhood SES and birth outcomes.