Why does natural resource wealth prolong incumbency? Using evidence from parliamentary elections in the Islamic Republic of Iran, the author shows that natural resource revenues boost incumbent reelection rates because they are used to provide public or private goods to constituents, which incentivizes voters to reelect incumbents over challengers. To test this hypothesis, the author employs originally assembled data on five parliamentary elections in Iran (1992–2008) in longitudinal hierarchical regression analyses at the district and province levels. By leveraging Iran's mixed-member electoral system, he shows that the resource-incumbency mechanism works primarily in single-member districts with little evidence of an incumbency advantage for politicians in resource-rich multimember districts. Building on the rentier theory of natural resource wealth, the results suggest that voting for the incumbent is attributable to patronage and public goods distribution. The findings offer new insights into the understudied context of Iranian legislative elections, illustrate the mechanisms driving the relationship between resource wealth and incumbency advantage at the subnational level in a nondemocratic setting, and highlight the mediating effects of electoral institutions on the resource-incumbency relationship.