Italy's parliament on Wednesday ratified the UN's Arms Trade Treaty, which is intended to stop arms supplies to countries at war or that abuse human rights.
The treaty was adopted by the United Nations in April to regulate the $80 billion (59 billion euros) annual trade in conventional arms and stop supplies to states where they could be used for human rights abuses.
"It is a great result," said Silvana Amati, a senator from the left-wing Democratic Party.
Amati said Italy could be "a driving force within the European Union, seeing as at least 50 countries need to ratify the treaty for it to enter into force."
Only four other UN members have ratified so far, and Italy is the first European Union state to do so.
Italy is the eighth biggest arms exporter in the world, according to the Stockholm International Peace Research Institute, which keeps detailed data.
Its handguns, high-precision artillery systems and attack helicopters are particularly prized, and it has in the past supplied arms to deposed Libyan dictator Muammar Gaddafi and Syrian President Bashar Al-Assad.
The treaty has no automatic enforcement but seeks to contain the weapons industry within accepted boundaries.
The treaty, which has been years in the making, was adopted only after tough negotiations at the United Nations.
US Secretary of State John Kerry is expected to sign the treaty later Wednesday, according to a US official, in a move that could help the West push Russia to curtail arms sales to Syria.