Drawing on trait activation theory, we examine a person-situation interactionist model to predict unethical behavior in organizations. In particular, we examine abusive supervision as a condition under which employee Machiavellianism (Mach) is activated and thus more strongly predicts unethical behavior. We offer a more fine-grained analysis of the Mach–trait activation process by specifically examining the interactive effect of each Mach dimension (viz., Distrust in Others, Desire for Control, Desire for Status, and Amoral Manipulation) and abusive supervision onto unethical behavior. We collected multisource field data to test our hypotheses across two studies. We then tested our theoretical model utilizing an experimental design. The results of our field studies indicate that the interaction of amoral manipulation and abusive supervision is the most predictive of unethical behavior, whereas our experimental findings indicate that the interaction of desire for control and abusive supervision is the primary predictor of unethical behavior. Implications for the Machiavellianism literature and trait activation theory are discussed.