Background: There is a strong research imperative to investigate efficacious treatment options for adolescents and adults with Autism Spectrum Disorder (ASD). Elevated social anxiety, difficulties with social functioning, and poor mental health have all been identified as core treatment targets for this group. While theoretical models posit a strong bidirectionality between social anxiety and ASD social functioning deficits, few interventions have targeted both domains concurrently. Of the two group interventions previously conducted with adolescents and adults with ASD, significant results have only been observed in either social anxiety or social functioning, and have not generalised to changes in overall mood. The aim of this study was to evaluate the efficacy of a group intervention in young adults with ASD. Primary treatment outcomes were social anxiety symptoms and social functioning difficulties; secondary outcomes were self-reported mood and overall distress. Method: Participants completed an eight-week, modified Cognitive Behavioural Therapy (CBT) group intervention targeting both social anxiety and social functioning. Sixty adolescents and young adults with ASD, without intellectual impairment, aged between 16 and 33 (M = 22.23; SD = 4.62), were recruited from the community, Headspace, and referrals to the Autism Clinic for Translational Research. Outcomes (social anxiety, social functioning and mood) were measured pre- and post-intervention via self-report questionnaires, and participants were invited to provide feedback on the intervention (at the mid-point and end of the intervention).Results: Participants demonstrated statistically significant improvements on all outcome measures in response to the intervention. Specifically, social anxiety symptoms decreased, and social functioning difficulties improved post intervention, particularly in overall social functioning, social awareness and restricted interests and repetitive behaviours. Self-reported symptom improvements also generalised to mood (depression, anxiety and stress). All improvements demonstrated small-to-medium effect sizes. Participant feedback was positive and indicated strong satisfaction with the program.Limitations: The absence of a control group and use of a randomized controlled trial, reliance on self-report instruments as outcome measures, and the exclusion of those with intellectual disability represent significant limitations to this study. Conclusions: These findings indicate that a group CBT intervention is an efficacious treatment for self-reported social anxiety, social functioning and overall mental health in adolescents and young adults with ASD. The standalone nature of the intervention combined with positive participant feedback indicates potential clinical utility, and warrants further study in a randomised-controlled, follow-up design.