An appeals court in Buenos Aires has convicted ex-President Carlos Menem of illegally selling 6,500 tonnes of arms to Croatia and Ecuador in the 1990s.
Both countries were at war and under arms embargoes at the time they bought the Argentine weapons.
Menem was originally acquitted of the charges in 2011.
Defence Minister Oscar Camilion and 10 other officials who had been acquitted along with him were also found guilty by the appeals court on Friday.
The 82-year-old, who was in office from 1989 to 1999, will be sentenced by a different court.
His lawyers said earlier they would appeal against his conviction, for which he faces between four and 12 years' imprisonment.
As a senator, he enjoys immunity from imprisonment but could be stripped of his status by parliament or jailed when his term expires next year, correspondents say.
'Panama and Venezuela'
The court found that there was no way the weapons could have been smuggled without Menem's approval as president.
Menem has admitted signing export papers for the arms but said he had no idea the arms would end up in Ecuador and Croatia.
He maintained that the shipments of rifles, anti-tank rockets and ammunition were bound for Panama and Venezuela when he authorised them.
Evidence about the true destinations first came to light in 1995. Menem was formally charged in October 2008.
The weapons that ended up in Croatia were sent in seven shipments between 1991 and 1995 when much of the Balkans was under a UN arms embargo.
Weapons arrived in Ecuador aboard three flights in February 1995 at a time when Ecuador was engaged in a border war with Peru.
Argentina - as one of the guarantors of a peace agreement between the two nations - was banned for selling arms to either side.