Recent waves of immigration in Western societies have drawn attention to social transformational challenges and their repercussions for migrant physical and mental wellbeing. Research into migration has tended to focus on Cultural Integration (CI) with Western country cultures and social norm. We fill a research gap in which the social transformation repercussions and the evolutionary function of human psychology remain underexplored. We theorize how the Evolutionary Fitness and Subjective Significance of Identity can emerge from CI, thus, positively impacting Subjective Well-Being (SWB) of migrants. To legitimize the model we propose, sets of rigorous empirical analyses were developed, drawing on panel data of 5,558 respondents from 7 waves of global migrant surveys within the UK during 2009–2018. Our results supported our hypotheses by suggesting that a tightly defined CI was negatively related to SWB, but a relatively fluid orientation towards CI was positively related to SWB, and the positive relationship became more compelling when the Subjective Significance of Identity (SSI) emerged from the integration process, such that the indirect effect of CI through SSI on SWB was strongest when the degree of SSI was high. Our study offers implications for how policymaking and management strategies can integrate cultural characteristics, increasing migrants’ cultural confidence, self-esteem, and economic creativity in the country of residence.