This study investigated the immediate effect of a Best Possible Self (BPS) intervention to enhance positive affect, situational academic motivation and academic commitment in a university context. A large sample of 176 French undergraduate students participated in the study. An experimental group (n = 88) performed a “Best Possible Self” (BPS) intervention that consisted of mentally thinking of the ideal academic future life. A control group (n = 88) was recruited to read neutral information during the same time. We evaluated positive and negative affect, situational academic motivation, and academic commitment. A comparison between the experimental and control group revealed significantly higher levels of positive affect, self-determined situational motivation, and academic commitment in the experimental group than in the control group. The results suggest that future positive thinking may be used to enhance situational academic motivation, and academic commitment in students, with a pivotal role for positive affect. Finally, the BPS intervention effect on motivation was fully mediate by positive affect.