IntroductionProfessionals are often required to perform tasks they regard as unnecessary or inconsistent with their legitimate responsibilities. Although research has linked such illegitimate tasks to adverse work outcomes, less is known about how they are associated with employees’ appraisal of the work–nonwork interface, motivational investment, and work role performance, or how leadership conditions this process. Drawing primarily on cognitive–affective personality system (CAPS) theory, we propose that illegitimate tasks operate as situational stimuli that activate employees’ work–life balance appraisals, which are associated with work engagement and, in turn, employee-reported work role performance. Work–family boundary theory is used to explain why authoritarian leadership strengthens the negative association between illegitimate tasks and work–life balance.MethodsUsing three-wave survey data from 615 engineering consulting professionals, we tested a moderated, theoretically ordered indirect-effects model examining the associations among illegitimate tasks, work–life balance, work engagement, employee-reported work role performance, and authoritarian leadership.ResultsIllegitimate tasks were negatively associated with work–life balance; work–life balance was positively associated with work engagement; and work engagement was positively associated with employee-reported work role performance. The serial indirect association through work–life balance and work engagement was negative and became stronger as authoritarian leadership increased.DiscussionThese findings identify work–life balance as one complementary cross-domain pathway through which illegitimate tasks may be associated with engagement and performance. They also show how CAPS accounts for the proposed stimulus–appraisal–motivation–performance process, whereas work–family boundary theory explains the leadership condition that strengthens its initial association. Because work–life balance and work engagement were assessed during the same survey wave, the findings support a theoretically ordered indirect association rather than a definitive temporal or causal sequence.