Background: The post-treatment period for childhood leukaemia survivors and their parents is a critical yet under-researched time, marked by challenges that impact quality of life. Social support is crucial for maintaining a good quality of life but tends to decline after treatment ends. Resilience, closely linked to social support, also plays a key role in maintaining well-being. However, few studies have explored the relationship between social support, resilience and quality of life among survivors and their parents. Aims: The study aims to gain a deeper understanding of the post-treatment experiences of childhood leukaemia survivors and their parents, focusing on the relationship between social support, resilience and quality of life. Methods: A systematic review of social support among child and adolescent cancer survivors was conducted. A convergent parallel mixed-methods design followed, combining cross-sectional surveys with 70 parents and 35 children and qualitative interviews with 19 parents and 11 children. Results: Quantitative findings showed that for parents, greater social support was linked to higher resilience and better mental well-being. For children, greater social support was associated with higher resilience, which in younger children related to better overall quality of life and psychosocial health, while in older children resilience was linked mainly to psychosocial health. Qualitative findings highlighted the emotional complexity of parents’ recovery and the developmentally diverse experiences of children. Integrative findings revealed survivorship as a dynamic, relational process, with longer time since treatment completion associated with lower levels of perceived support, despite persistent emotional and practical needs. Conclusions: The post-treatment period is complex and evolving. Sustained, developmentally tailored support is needed to promote resilience and quality of life. Care delivery should incorporate routine psychosocial screening and timely interventions, and policy should embed structured survivorship care pathways to ensure equitable, ongoing access to psychosocial support.