Power and aggression are core relational variables that share a fickle relationship. It is unclear whether high or low power relates to psychological aggression and under which circumstances. We tested psychopathy as a potential moderator in the power-aggression link because psychopathy is characterized by a lack of empathy and shallow emotional response. Psychopathy could strengthen the link between high power and psychological aggression because power ignites character traits and their corresponding behavior. Alternatively, psychopathy could strengthen the link between low power and psychological aggression because individuals high in psychopathy may attempt to compensate for their lack of power with aggression. We tested these competing hypotheses in a romantic context across two studies (N1 = 188 individuals, N2 = 226 couples). We found power to be negatively related to both actors' and partners' psychological aggression. Supporting the latter hypothesis, we found that the most psychologically aggressive people had low power and high psychopathy. In addition, people reported high psychological aggression when their partners were low in power and high in psychopathy. These findings advance existing power theories and research by highlighting how personality traits such as psychopathy affect both intra- and interpersonal links to psychological aggression.