People Before Profit-Solidarity TD Paul Murphy has confirmed he will take part in a planned flotilla seeking to gain access to Gaza next week.
Pro-Palestinian activists are preparing to set sail from Barcelona on Sunday for Gaza in dozens of boats carrying aid.
They have called on governments to pressure Israel to allow their flotilla - the largest to date - through the naval blockade.
Swedish activist Greta Thunberg and Portuguese left-wing politician Mariana Mortagua are among hundreds of people from 44 countries due to depart from several ports to Gaza as part of the Global Sumud Flotilla.
Sumud means "perseverance" in Arabic.
Speaking to reporters at Leinster House, Deputy Murphy said he will travel to Tunis in Tunisia to join the flotilla.
He said the flotilla will depart Tunis on Thursday and is likely to include 50 boats and more than 1,000 people.
Deputy Murphy said the reason for the flotilla is to try to break the Israeli embargo on Gaza, to provide humanitarian aid to those in need and to address the "horrifying unfolding nightmare of genocide" in Palestine.
Mr Murphy was detained in June in Egypt while en route to reach Rafah on a Gaza peace march.
Global Movement to Gaza said some Irish citizens will crew boats to Gaza while many more will work from Ireland to ensure the mission's success.
Galway poet Sarah Clancy will be part of the Irish delegation setting sail from Barcelona on Sunday.
"I want the Palestinian people trapped in Gaza to know that we refuse to be silent. I want our governments to know that if they don't act, we will," she said.
Israel has scuppered numerous attempts over the 15 years of the blockade, including a 2010 boarding by its special forces in which at least nine Turkish activists were killed.
The ball was in politicians' court to put pressure on Israel to let the flotilla through, said Saif Abukeshek, one of the organisers.
"They need to act to defend human rights and to guarantee a safe passage for this flotilla," the Palestinian, who is resident in Spain, said in Barcelona.
In June, Israeli naval forces boarded and seized a British-flagged yacht carrying Ms Thunberg, among others.
Israel has imposed a naval blockade on the coastal enclave since Hamas took control of Gaza in 2007, saying it aims to stop weapons from reaching the militant group.
Israeli attacks have killed almost 63,000 Palestinians since October 2023, according to health officials in Gaza, while a global hunger monitor says part of it is suffering from famine.
UN human rights chief Volker Turk said the famine was the direct result of Israeli government policies.
The current stage of the war began when Hamas-led militants rampaged through southern Israel on 7 October 2023, killing more than 1,200 people and taking 251 hostages, according to Israeli tallies.
In early March, Israel also sealed off Gaza by land, letting in no supplies for three months, arguing that Hamas was diverting aid.
Additional reporting Fiachra Ó Cionnaith
