Families often undergo separations during the migration process. A body of literature has explored the consequences of these separations for children “left behind” and, more recently, children reunified with their parents at the destination. However, little attention has been given to whether this experience during childhood is associated with well‐being into adulthood. This paper adopts a life course perspective to explore well‐being amongst youth (18–25 years) who migrated as children to the UK and France. Drawing on national household surveys, Understanding Society (UK) and Trajectories and Origins (France), we analyse whether which of the parents migrated and whether the young person migrated with them or experienced a period of separation are associated with self‐rated health (both countries) and mental well‐being (UK) or conflict with parents (France). Our findings show that whilst the majority of youth migrated with their parents (86% in the UK and 69% in France), those who did experience long‐term parental separation (6+ years) have poorer psychosocial well‐being in both destinations. This suggests that disruption to the parent–child relationship amplifies the risk of poorer outcomes in early adulthood and highlights that the context of family migration is not only important for understanding migrants' well‐being during childhood, but also as they progress into adulthood.