A neighbour of the monastery called authorities after seeing a man throwing bags on to the property near Buenos Aires early on Tuesday.
Officers arrived and arrested a man who turned out to be the former secretary of public works, Jose Lopez.
Police initially detained him for possession of a .22 calibre rifle.
They then discovered wads of cash as well as watches in more than 160 packages inside the bags. Other money had been taken to the monastery kitchen and some was found in the boot of a car.
Security minister Cristian Ritondo, of Buenos Aires province, told a news conference that Lopez was “in a state of shock” when he was arrested and alleged that he tried to bribe police.
“He later told the nuns that police had tried to steal the money that he was trying to donate,” Ritondo said. “There are dollars, yen, euros and a currency from Qatar. It’s a lot of money.”
He did not give an exact amount because the money was still being counted.
Dario Kubar, the area’s mayor, said that authorities had found more than $7 million at the monastery that is home to nuns devoted to Our Lady of the Rosary of Fatima, which is about 35 miles west of Buenos Aires.
The news became a trending topic on Twitter in Argentina. Local TV stations showed images of the piles of cash, and later of Lopez being escorted by police to another precinct wearing a helmet and a bulletproof vest.
Marcos Pena, President Mauricio Macri’s Cabinet chief, said: “It’s almost out of a movie. We’re shocked because it’s not a minor official. He led public works, which were so questioned, where we saw so much daily corruption.”
Since Fernandez ended her term in December, Macri’s administration has promised to root out corruption that has plagued Argentina.