Human society and its development are based on the principle of cooperation. The choice of a cooperative strategy in a context of uncertainty, such as the iterated Prisoner’s Dilemma game, can be influenced by many factors, both individual and situational. However, there is limited evidence regarding how these factors affect strategic choices when players are subjected to cognitive load conditions. The aim of this study was to investigate the effects of situational factors, such as cognitive load, and two individual factors, namely peace attitude and personality, on strategic decision-making. Fifty-six adults participated in the iterated Prisoner’s Dilemma game under two conditions that differed in cognitive load: in the first condition, they had to make decisions about the Prisoner’s Dilemma task with working memory load, while in the second condition, they had to make decisions about the same task without working memory load. Additionally, participants completed the Peace Attitude Scale and the Italian 10-Item Big Five Inventory. The results indicated that both individual and situational factors influenced strategic choices. Specifically, cognitive load increased the cooperative strategy in the iterated Prisoner’s Dilemma game. Furthermore, individual factors influenced strategic choices only in the condition with cognitive load: people with higher levels of peace attitude and conscientiousness tended to be more cooperative than those with lower peace attitude.