Micheal Martin's comments came as the Irish parliament passed a non-binding motion agreeing that "genocide is being perpetrated before our eyes by Israel in Gaza".
South Africa in December brought a case before the ICJ, arguing that the war in Gaza breached the 1948 United Nations Genocide Convention, an accusation Israel has strongly denied.
Several nations have added their weight to the proceedings, including Spain, Bolivia, Colombia, Mexico, Turkey, Chile and Libya.
Ireland had said it would file a submission to the court once South Africa had submitted a document supporting its claims, which it did on Monday.
"The government's decision to intervene in the South African case was based on detailed and rigorous legal analysis," Martin told lawmakers in the Irish parliament, the Dail.
"Ireland is a strong supporter of the work of the court and is deeply committed to international law and accountability."
South Africa announced on Monday that it had filed a so-called memorial with the ICJ claiming "evidence" of a "genocide" committed by Israel in the Gaza Strip.
The document cannot be made public but was "over 750 pages of text, supported by exhibits and annexes of over 4,000 pages", said the office of President Cyril Ramaphosa.
An official for The Hague-based court on Monday confirmed it had received the document, but declined to give further details.
Ireland has been among the most outspoken critics of Israel's response to the October 7, 2023 attacks by Hamas that sparked the latest round of violence across the region.
Irish government parties did not oppose a symbolic motion brought by opposition groups on Thursday accusing Israel of genocide against Palestinians, meaning it passed during a sparsely attended session.
On Tuesday, Ireland confirmed the appointment of a full Palestinian ambassador for the first time, after Dublin formally recognised a Palestinian state earlier this year.
Ambassador Jilan Wahba Abdalmajid told the Irish Times in an interview published on Thursday that Israel should be suspended from the UN for cutting ties with the body's aid agency for Palestinians, UNRWA.
"If you are a member of the UN and you do not abide by the rules of this organisation then what is the meaning of being a member?" she was quoted as saying.
Failure to suspend Israel would allow other nations to follow suit, added Abdalmajid, whose parents taught in UNRWA-run schools in Gaza.
