Objectives: The present study was designed to find a systematic answer to the question of what is the relationship between Iranians' religious commitment and their assessment of the legitimacy of the Islamic Republic government? In this regard, by reviewing the literature in the subfields of sociology of religion and political sociology and making some arguments, it was hypothesized that Iranians' religious commitment has a positive correlation with their assessment of the legitimacy of the Islamic Republic government. Study Method: This study used data from the third wave of the National Survey of Iranian Values and Attitudes for a secondary analysis on the relationship between Iranians' religious commitment and the legitimacy of the Islamic Republic government. Findings: The results of this study indicated empirical support for the research hypothesis among Iranian Muslims, in such a way that all statistical analyses showed that the two constructs of "religious commitment" and "political legitimacy" had a relatively strong positive relationship with each other, and this significant relationship remained even after controlling for or eliminating the effect of background variables. Conclusion: The results of this study can be considered as confirmation that in Iranian society, individuals' religious commitment as an identity-belief characteristic can have an important political function in granting legitimacy to the government institution. So it can be said that religion in the post-revolutionary Iran is still a source of legitimacy for the Islamic Republic government and, in turn, a source for maintaining and continuing political stability.