When parents migrate, they often leave children behind with relatives. Despite being at higher risk of socio-emotional problems, many left-behind children have good health and social outcomes, suggesting their resilience. We sought to understand how adolescents with internal and international migrant parents build resilience in Thailand. We conducted qualitative interviews with 24 adolescents aged 10-19, and six caregivers, parents and community leaders. Interviews were transcribed, translated and analysed, drawing on techniques from grounded theory. We found that resilience was built in a context where for many families, migration was a financial necessity and the parent-child relationship was mainly phone-based. Adolescents built resilience using three key 'resources': warmth (love and understanding), financial support and guidance. Adolescents with insecure parent or caregiver relationships, or with caring responsibilities for relatives, were less likely to have access to these resources. These adolescents sought emotional and financial independence, prioritised friendships and identified role models to obtain key resources and build resilience. The findings indicate practical and psychosocial barriers to building resilience among left-behind adolescents in Thailand. Further work could explore pathways to mental illness in this population, interventions that build peer networks and caregiver-child relationships and the use of technology to support remote parenting.