Argentine prosecutors believe Iran's government ordered the 1994 Jewish center bombing that killed 85 people, and put a list of high-ranking Iranian officials on Interpol's watch list for years. Iran denies any role in the bombing, and has never allowed the suspects to be questioned.
The treaty would set up an independent "truth commission" and enable Argentina's prosecutors to interrogate the Iranian suspects in Teheran.
President Cristina Fernandez's government controls both houses of congress, where the treaty got final approval early Thursday after a heated debate. Now it goes to Iran's parliament.
Israel has criticized the effort, and Argentina's Jewish organizations have largely come out against it as well, doubting that Iran can be trusted.
"Don't betray the memory of the victims. No to the accord with Iran," read one of many banners in the crowd that held vigil before the 131-113 vote in the lower house of Congress early Thursday.
At times, the debate descended into screaming matches between opponents of the Fernandez government and her foreign minister Hector Timerman, who signed the proposed treaty with his Iranian counterpart. Some lawmakers accused Timerman, who is Jewish, of being a traitor both to his country and his faith.
"It is clear that none of you ever lost anyone in the Holocaust," Timerman yelled back. "You should be ashamed of yourselves. You deeply offended my soul."