This article contributes by offering a comprehensive exploration of the ways in which social workers support the well-being of service users with an immigrant background. The research question is how the well-being of the service users emerges from the content of the social work process and its context. The study encompasses two datasets: service user documents and service user interviews. The explanatory approach is predicated on critical realism as a theoretical framework, with a particular emphasis on CAIMeR theory. A critical realist analysis was conducted, which resulted in the identification of three social mechanisms that enable the well-being of service users: supportive, response, and holding. The activation of these mechanisms occurs in the interaction between social worker and service user, and these interactions influence the subjective well-being of service users with an immigrant background. The supportive and holding mechanisms play a pivotal role in the stalling and stagnant improvement of service user’s well-being. An important implication of the study is understanding of the interconnectedness of well-being and integration, as well as their manifestations at the micro-, meso-, macro-, and transnational levels.