People with autism spectrum disorder (ASD) have an increased risk of suicidality. However, the risk factors remain under-investigated. This study explored factors that increase suicidality risk in ASD. Through an online survey, 150 adults with ASD were compared to 189 control adults. Autistic traits, depressive symptomatology, alexithymia, and antidepressant intake were assessed on their contribution predicting suicidality. Among people with ASD, 63% scored above the cutoff for high suicidality risk. Increased autistic traits, depressive symptomatology, and antidepressant intake significantly predicted suicidality. Furthermore, among those with high levels of autistic traits, the risk of suicidality was increased if they also had high levels of alexithymia. These results highlight the importance of considering depression, antidepressants, and alexithymia to prevent suicidality in ASD.