Background  Although the promotion of social inclusion through sports has received increased attention with other disadvantaged groups, this is not the case for children and adults with intellectual disability who experience marked social isolation. The study evaluated the outcomes from one sports programme with particular reference to the processes that were perceived to enhance social inclusion.Method  The Youth Unified Sports programme of Special Olympics combines players with intellectual disabilities (called athletes) and those without intellectual disabilities (called partners) of similar skill level in the same sports teams for training and competition. Alongside the development of sporting skills, the programme offers athletes a platform to socialise with peers and to take part in the life of their community. Unified football and basketball teams from five countries – Germany, Hungary, Poland, Serbia and Ukraine – participated. Individual and group interviews were held with athletes, partners, coaches, parents and community leaders: totalling around 40 informants per country.Results  Qualitative data analysis identified four thematic processes that were perceived by informants across all countries and the two sports to facilitate social inclusion of athletes. These were: (1) the personal development of athletes and partners; (2) the creation of inclusive and equal bonds; (3) the promotion of positive perceptions of athletes; and (4) building alliances within local communities.Conclusions  Unified Sports does provide a vehicle for promoting the social inclusion of people with intellectual disabilities that is theoretically credible in terms of social capital scholarship and which contains lessons for advancing social inclusion in other contexts. Nonetheless, certain limitations are identified that require further consideration to enhance athletes' social inclusion in the wider community.