This study explored whether the Interpersonal Theory of suicide informs our understanding of high rates of suicidality in autistic adults. Autistic and non-autistic adults (n = 695, mean age 41.7 years, 58% female) completed an online survey of self-reported thwarted belonging, perceived burden, autistic traits, suicidal capability, trauma, and lifetime suicidality. Autistic people reported stronger feelings of perceived burden, thwarted belonging and more lifetime trauma than non-autistic people. The hypothesised interaction between burdensomeness and thwarted belonging were observed in the non-autistic group but not in the autistic group. In both groups autistic traits influenced suicidality through burdensomeness/thwarted belonging. Promoting self-worth and social inclusion are important for suicide prevention and future research should explore how these are experienced and expressed by autistic people.