Objective: Following acquired brain injury (ABI), young people may experience increased anxiety as well as difficulties with their psychosocial functioning. This study examined trait mindfulness as a mediator of the relationship between anxiety and psychosocial domains of School and Leisure Activities (SLA), Interpersonal Relationships (IR) and Daily Living Skills (DLS). Method: Participants were adolescents with ABI (aged 12–19 years, N = 38). Standardised measures were used to assess anxiety, trait mindfulness, and psychosocial functioning. Results: Higher levels of anxiety were found to be associated with reduced IR (p <.05) and DLS (p <.05). Increased trait mindfulness was found to be associated with lowered anxiety (p <.01), as well as with better IR (p <.05) and DLS (p <.01). Mediation analyses found a significant indirect effect for the relationship between anxiety and DLS through trait mindfulness. Conclusion: Findings highlight the contribution of trait mindfulness as a mediator between anxiety and psychosocial functioning, such that increased mindfulness and lower levels of anxiety are related to better DLS.