Immigrants and their descendants constitute an increasing share of European populations, yet research on how immigrant background shapes the cohabitation experience remains limited. This study investigates how generational status at the individual level and national context at the macro level influence the likelihood of ever having cohabited. Our central proposition is that the diffusion of cohabitation among immigrants is more pronounced in countries where the practice is common and socially accepted among the native population. We analysed pooled data from the European Social Survey (ESS; 2002–2023), encompassing 66,017 respondents across 32 countries. Our findings provide evidence of an adaptation pattern: descendants of immigrants are significantly more likely to have ever cohabited than the first generation. Crucially, this generational difference does not vary systematically according to the prevalence of cohabitation among natives. The cohabitation context nonetheless significantly increases the likelihood of ever having cohabited, outweighing the influence of economic factors such as income inequality (Gini index). This suggests that the social and normative environment—the cohabitation context—is a primary driver of behavioural change. This study contributes to the literature by demonstrating that immigrant family formation is not merely a product of individual traits but is fundamentally shaped by the normative climate of the host country.