The attacker drove up to the entrance situated at the July 14 bridge across the Tigris River from the Green Zone before detonating an explosives-rigged vehicle, an interior ministry official said.
The blast killed seven people and wounded at least 24, according to the official and a medical source. MP Habib Hamza al-Turfi was among those wounded, another deputy, Ammar Toma, told AFP.
The Green Zone is among the most heavily fortified areas in Iraq, surrounded by heavy concrete blast walls and guarded by Iraqi soldiers armed with equipment ranging from assault rifles to US-made Abrams tanks.
While violence in Iraq is down from its peak in 2006 and 2007, attacks are near-daily occurrences and insurgents have shown they can strike at even the most highly-secured sites.