Background The interpersonal-psychological theory of suicidal behavior (IPTS) posits that the joint presence of perceived burdensomeness (PB), thwarted belongingness (TB), and capability for suicide (CS) is necessary for suicide attempt. Emerging evidence demonstrates these effects are not consistently observed. Psychopathology may independently impact on the explanatory power of the IPTS constructs. Aims The aims of the current study were to assess whether the inclusion of psychopathology indicators into the IPTS explains additional variance in recent suicide attempt and to assess the relative influence of interpersonal-psychological constructs versus mental illness on suicide attempt. Method Australian adults (N = 1,323; 77% female) who reported suicidal ideation in the past year were recruited using social media advertising to complete an online cross-sectional survey. Results None of the predicted IPTS interactions was significantly associated with recent suicide attempt, although PB and CS had significant independent associations. The addition of psychopathology indicators to the IPTS model explained significant additional variation in suicide attempt (18% vs. 14%). Conclusions The influence of psychopathology on suicide attempt may be insufficiently explained by interpersonal-psychological constructs. The IPTS may have greater explanatory power to identify transitions from suicidal ideation to suicide attempt after accounting for mental illness.