Conscientious individuals tend to be achievement, detail and planning-oriented. Several studies have found a consistent relationship between conscientiousness and overall job performance, leader emergence, and leader effectiveness. Yet, despite these positive connotations, the relationship between leader conscientiousness and abusive supervision remains controversial and empirical studies fail to draw a unanimous conclusion. Several studies argue that conscientious leaders tend to create a fair environment for their employees and engage in ethical leadership behavior. Others argue that the trait of conscientiousness may play a role in the emergence of abusive supervision since conscientious supervisors are highly goal-achievement oriented and may engage in abusive supervision due to performance-driven motives. Failing to figure out the above relationship is detrimental considering that conscientious individuals are more likely to get promoted. Accordingly, our goal in the present research is to shed light on the relationship between leader conscientiousness and abusive supervision in light of existing debates in the personality approach to leadership. We use conservation of resource theory (COR) as an overarching theoretical framework for the current investigation. COR theory is particularly relevant to our investigation because it inherently states what individuals do when confronted with stress and when not confronted with stress, which helps understand the processes and conditions under which conscientious leaders are more likely to abuse subordinates. In line with COR, we propose that the relationship between leader conscientiousness and abusive supervision is conditioned by environmental uncertainty. We also focus on leaders’ feelings of emotional exhaustion, a state reflecting resource depletion, as an immediate consequence of the joint effect of leader conscientiousness and environmental uncertainty. Two-wave data collected from 389 employees and 95 supervisors showed that: Environmental uncertainty moderated the relationship between leader conscientiousness and abusive supervision. Environmental uncertainty can also moderate the relationship between leader conscientiousness and emotional exhaustion. Emotional exhaustion was positively associated with abusive supervision. The indirect effect of leader conscientiousness on abusive supervision via emotional exhaustion was conditional upon environmental uncertainty, such that the indirect effect became increasingly positive as environmental uncertainty increases and increasingly negative as environmental uncertainty decreases. Our research offers three major contributions. Firstly, we extend understandings regarding the previously unclear relationship between leader conscientiousness and abusive supervision. Acknowledging that leader conscientiousness may not have straightforward effects on abusive supervision, we explore the possibility that other factors may condition this relationship. To this end, the second theoretical contribution is that our study answer calls to identify situational factors (i.e., environmental uncertainty) that interact with leader personality to predict both proximal and distal outcomes. Our focus on environmental uncertainty (a boundary condition) and emotional exhaustion (a mediating mechanism) are particularly useful given that popular press attention for both constructs has so far outpaced scholarly investigations. Finally, our study adds to the relatively scant literature examining leader personality as antecedents of abusive supervision and, related, provides needed attention for how intrapersonal factors affect abusive supervision.