We explore, using a unique survey dataset containing retrospective information on immigrants’ legal status, the relationship between previous irregular experience—from arrival up to the first residence permit achievement—and fertility patterns among non-EU immigrant women in Italy. While competing hypotheses explaining migrants’ fertility behaviour have been recurrently offered, there is a substantial lack of knowledge on the role of undocumented experience as a contextual barrier in shaping international migrants’ family formation processes. We adopt a life-course approach, employing event history analysis and Poisson regression modelling, to investigate how irregularity among immigrant women intertwines with the timing of the first childbirth and the total number of births occurred in Italy. We find that irregular experience—as a time-dependent process—delays the transition to childbirth post-migration. Furthermore, having experienced irregular status reduces completed fertility, offering few possibilities to catch-up over the life-course with fertility levels of women continuously having the legal status. Findings suggest long-lasting effects of irregular status and the potential disruption of migrant’s fertility induced by migration policies, admission systems, and regulation factors. The reduced possibility of legal entry channels and lack of migration policies for planning and managing migration into Italy may thus have an impact on family formation trajectories among international immigrant women.