Using games as part of the intervention and support process (sometimes referred to as 'gaming therapy') is an increasingly popular method of supporting autistic youth to develop social competencies and other skills because they are believed to be inherently motivating and fun for youth. Some emerging research has indicated that intervention programmes using games can be beneficial for autistic youth, but little is currently known about why, how and for whom they work. This study conducted a realist evaluation of a programme using the video game "Minecraft" for autistic youth, comprising interviews and observations with autistic youth (n = 4), facilitators (n = 2) and caregivers (n = 6). Findings from interviews and observations suggest that leveraging strengths, sharing power by placing youth in the 'expert role' and learning in a naturalistic and motivating environment provided youth with the opportunities to develop social competencies in communicating their wants and needs and supported the development of social connections, independence and emotion regulation. The results of this realist evaluation may provide a framework for future intervention and support programmes using video games.