© 2018 The objective of this study was to investigate potential mediating effects of health-related quality of life between children's participation in organised sports and measures of adiposity. The sample consisted of 4116 children derived from the Longitudinal Study of Australian Children. Participants were aged 10.32 (SD = 0.47) years at baseline (2010), and followed up 24 and 48 months later. Participation in organised sports was assessed using child-completed time-use diary. Health-related quality of life and demographic data were reported by each child's primary parent. Measures of body mass index, body fat, and waist circumference were also taken at each Wave. Sport was indirectly associated with measures of body fat (β = −0.002, 95%CI −0.004, 0.000, p =.039) and waist circumference (β = −0.001, 95%CI −0.003, 0.000, p =.039) through the mediating effects of social functioning. Sport was also associated with body fat via physical functioning (β = −0.01, 95%CI −0.02, −0.003, p =.038), however, this was not replicated with other measures of adiposity. No other mediating effects were evident. Sport participation may enable children and adolescents to function well in groups and access social support which in turn promote health behaviours and influence adiposity. This may be one of multiple pathways through which sports participation is associated with adiposity. Replication and extension of these novel findings is warranted, as is a focus on the design and implementation of sports programs to maximise health benefits.