Adults with autism spectrum disorder (ASD) often experience social marginalisation. This study uses a vignette-based design to clarify whether diagnostic disclosure affects social marginalisation in workplace contexts. It investigates two potential mediators of this relationship: affective response to and theory of mind for people with ASD. Participants (n = 170) read a description of a hypothetical co-worker with ASD traits, whose diagnosis was either disclosed or concealed. Providing a diagnostic label significantly reduced participants’ desire to socially distance themselves from the target. This effect was mediated by positive affective responses. Diagnostic disclosure did not influence theory of mind for people with ASD but did increase tendencies to attribute primary emotions to the target; however, this did not relate to social distance outcomes.