The pre-deal phase of an acquisition is complex, with high stakes, and high uncertainty. Consequently, acquisition decision making can be seen as an inherently political process. While political behavior is a central concept in organizational theory, and despite its inevitability during acquisition decision making due to the contested nature of the pre-deal phase, there is a shortage of theory and evidence concerning the antecedents, consequences, and moderators of political behavior. To address these theoretical shortcomings, we develop and test a theoretical model of political behavior focusing on the TMT’s psychological context. We argue that while political behavior risks undermining acquisition performance, the degree of board involvement during the pre-deal phase can enable some TMTs to attenuate the damaging effects of political behavior. Further, we theorize two key antecedents variously fueling and constraining political behavior. We contend that while TMT cohesion reduces political behavior, cognitive diversity increases political behavior while suppressing the potential for TMT cohesion to prevent political behavior. We test our theoretical model using a field-based sample of 109 UK acquisitions, combining multiple informants with objective secondary data.