The driver, a Paraguayan national, was held for questioning.
Daniel Scioli, the governor of Buenos Aires province, called it the "largest seizure in the history" of his country.
Scioli will face a conservative rival, Mauricio Macri, in a run-off for the Argentine presidency on November 22.
The police operation today took place in San Isidro, a northern suburb of the Argentine capital and one of the wealthiest neighborhoods in the region.
Police had seized a total of 15 tons of Paraguayan marijuana in three operations in northeastern Argentina in September and early October. Investigators say they believe the drug was being taken to the outskirts of Buenos Aires.
The drugs are often sent on to Chile or Brazil, or in some cases to Africa for eventual sale in Europe.