This research analyzes the expansion of Iranian influence in the Middle East after the 2000s and its relationships with the history of movements in the transnational Shia community. Throughout the history, there has been movements of people among Shias in the Middle East, particularly in Iraq, Iran, and the Gulf region. In the 20th century, the mobility and connectivity of this transnational Shia community enabled Shia Islamism to be spread, and contributed to the creation of pro-Iran factions following the leadership of the Iranian regime among Arab Shias. Iran uses the network of Arab Shia allies for expanding its influence in geopolitical competitions. This research argues that the movements of people in the transnational community, which have disseminated Iran’s ideologies and worldviews to Arab Shias, are related with the expansion of Iranian influence. The Shia identity, which has been strengthened by the mobility and connectivity of people in the transnational community, is one of key factors explaining Iranian influence in the contemporary Middle East.