Despite the efforts of mainstreaming in sports, inclusive participation of people with Intellectual Disabilities (ID) in sports remains challenging. In sports settings, the social environment may influence the motivation of athletes and promote (or restrict) inclusive sports participation of athletes with ID. Thus, this study aims to explore the motivations of athletes and coaches and to investigate the role of the social environment in sports participation of athletes with and without ID. Coaches who coach athletes with ID (n = 11), athletes without ID (n = 13) and both groups (n = 2) were involved in semi-structured interviews. From the inductive thematic analysis three themes were identified for the sports motivations of athletes with ID (Sport-related Progression, Social Interaction, Positive Emotions), two for their coaches’ motivations (Help others, Personal and Professional Development) and four for coaching practices toward athletes with ID (Psychological and Life skills development, Building Meaningful Relationships, Behaviour adaptations and Participation-focused). Moreover, ‘Teammates and Opponents’ and ‘Family’ were classified as social agents that influence the sport participation of athletes with ID. Coaches of athletes without ID reported additional themes about their athletes’ motivations (Health-related Reasons), their coaching motivations (Career aspirations) and their coaching practices towards athletes without ID (Performance-focused). The motivations of athletes and the practices of coaches could promote sports participation of athletes with ID, but more work is needed to address athletes’ sports motivations and overcome the able-ist attitudes and the social oppression that may make their inclusion in sports more challenging. These sports participation barriers and facilitators could provide direction to stakeholders for developing inclusive sports pathways to people with ID.