Extremism occurs when a certain need, for instance, significance quest, overrides other human motivations. Based on the Significance Quest Theory, we argue that ambition—a specific aspect of significance quest—can lead to extremism, particularly through obsessive passion. In an Italian sample (Study 1, N = 249) we predicted and found that ambition was positively related to both obsessive and harmonious passion; however, only obsessive passion positively predicted extremism. To bolster and generalize our findings we conducted a second study involving American participants (Study 2, N = 300). We confirmed the mediating role of obsessive passion in the relationship between ambition and extremism, while we did not find the mediating role of harmonious passion. The present research has theoretical implications in that it constitutes the first evidence that ambition might share some aspects with significance quest and sheds new light on ambition field. Moreover, our findings provide practical ways to prevent extremism.