We present a meta-analytic investigation of the theoretical mechanisms underlying why experienced workplace aggression is harmful to the three core performance outcomes (i.e., task performance, citizenship behavior, and deviant behavior). Through a comprehensive literature review of 405 empirical articles, we first extract and identify five prominent theoretical mechanisms: relationship quality, justice perception, psychological strain, negative affect, and state self-evaluation. By synthesizing evidence from these articles, which include 471 unique samples from 36 countries or regions (N = 149,341 participants), we reveal the incremental effects of the five mechanisms, compare their relative strengths for each performance outcome, and examine their cultural contingencies. We find that when the five mechanisms are examined simultaneously, only relationship quality and state self-evaluation show incremental effects across all performance outcomes in the predicted direction. Moreover, the comparative strengths of mechanisms vary across performance outcomes: The impact of workplace aggression on task performance is best explained by the negative affect and state self-evaluation mechanisms, its impact on citizenship behavior is best explained by the relationship quality mechanism, and its impact on deviant behavior is best explained by the negative affect mechanism. Finally, the prominence of some mechanisms is contingent on certain cultural dimensions: The relationship quality mechanism is strengthened by individualism and masculinity, while the state self-evaluation mechanism is strengthened by masculinity. We conclude with a discussion of the theoretical and practical implications of our research.