Job demands typical of the current working environments and negative leadership styles may be considered unsustainable factors able to decrease workers well-being. Moreover, contrary to the idea that workaholism is an innate individual characteristic, a recent perspective considers the working context able to foster its insurgence. In order to investigate unsustainable dynamics within organizations, this study aimed at examining whether (1) destructive leadership increases workload and supplemental work supported by technology, (2) the three job demands increases workaholism, and (3) workaholism mediates their relationship with exhaustion. A convenience sample of 432 workers filled in a self-report questionnaire. The structural equation model results showed a positive relationship between destructive leadership and workload, off-work hour Technology-Assisted Job Demand (off-TAJD), and workaholism. Moreover, both workload and off-TAJD partially mediated the relationship between destructive leadership and workaholism. Finally, workaholism was a mediator between the three demands and exhaustion. The study confirmed a positive association between job demands and workaholism, and, in turn, their association with exhaustion, highlighting in particular the role of two under-investigated determinants, namely destructive leadership and off-TAJD, as unsustainable working conditions. Despite limitations, above all the cross-sectional design, this study provided useful indications for research and practice.