Aims: Few studies have examined how the settlement experiences of migrant parents might impact on the downstream adult health of second-generation minority ethnic children. We used prospective data to establish if childhood adversity relating to the settlement experiences of Irish-born parents might account for downstream adverse health-related behaviours in second-generation Irish respondents in adulthood. Design, setting and participants: Cohort data from the National Child Development Study, comprising 17 000 births from a single week in 1958, from Britain, were analysed. Respondents were followed to mid-life. Dependent variables were alcohol and tobacco use. The contribution of life-course experiences in accounting for health-related behaviours was examined. Findings: Relative to the rest of the cohort, the prevalence of harmful/hazardous alcohol use was elevated in early adulthood for second-generation men and women, although it reduced by age 42. Second-generation Irish men were more likely to report binge alcohol use (odds ratio 1.45; 95% confidence interval 0.99, 2.11; P = 0.05), and second-generation Irish women were more likely to smoke (odds ratio 1.67; 95% confidence interval 1.23, 2.23; P = 0.001), at mid-life. Childhood disadvantage partially mediated associations between second-generation Irish status and mid-life alcohol and tobacco use, although these were modest for associations with smoking in Irish women. Conclusions: The findings suggest mechanisms for the intergenerational ‘transmission’ of health disadvantage in migrant groups, across generations. More attention needs to focus on the public health legacy of inequalities transferring from one migrant generation to the next.