The underlying mechanisms by which social support exerts its (typically) positive effects on parental wellbeing are still being investigated in the autism spectrum disorder (ASD) context. Parents (n = 674) of a child with ASD responded to questions probing parenting stress, parent psychological health, their child’s ASD symptoms, and the types of social supports they were currently utilising. Hierarchical multiple linear regression analyses examined whether social support moderated or mediated (or neither) the relationships between: (a) parent-rated child ASD symptoms and parenting stress, and (b) parenting stress and parent psychological health. The main findings were that none of the mediating models reached statistical significance, while 7/20 moderation analyses were significant, though significance was dependent upon how social support was operationalised.