Three others were injured in the incident near the village of Al-Aqbiya.
An Irish UN peacekeeping soldier has been killed after a "serious incident" in Lebanon, the foreign ministry said.
Several others were wounded -- including three soldiers in a serious condition.
Irish and Lebanese military officials said that unidentified attackers had opened fire on a convoy on Wednesday night.
The Irish Defense Forces said in a statement said that two armoured vehicles -- carrying eight Irish United Nations Interim Force in Lebanon (UNIFIL) peacekeeping troops -- were driving toward Beirut near the village of Al-Aqbiya.
UNIFIL also confirmed that one peacekeeper was killed and three wounded.
“Our thoughts are also with the local civilians who may have been injured or frightened during the incident,” spokesperson Andrea Tenenti said, adding that “details are sparse and conflicting”.
A military investigation is underway to “determine exactly what happened”.
Irish Taoiseach Micheál Martin -- who heads up the government -- expressed his condolences in a statement on Twitter.
“It is a reminder that our peacekeepers serve in dangerous circumstances, at all times, in the cause of peace,” he said.
UNIFIL, which has been stationed in Lebanon since Israel's 1978 invasion, is made up of nearly 10,000 soldiers from different contingents.
Clashes have previously occurred between UNIFIL patrols and pro-Iranian Hezbollah supporters, who regard the peackeepers' presence in the country as a "violation of Lebanese sovereignty".
In January, Irish UNIFIL peacekeepers were attacked by assailants in the southern Lebanese town of Bint Jbeil, with their vehicles vandalised and items stolen.
Local residents had accused the troops of taking photographs of residential homes, though the UN denied this.
Lebanon's caretaker prime minister Najib Mikati said on Friday that investigations into the killing were ongoing, adding that those responsible "will be punished".