Fr Willie Doyle was killed in the war while trying to help injured and dying soldiers, serving the army on battlefields including the Somme, Messines, and Passchendaele.
On Sunday, the Dubliner is receiving a special service in Mullingar before thousands of documents are sent to the Vatican to support the case for his canonization.
Doyle was said to have incredible courage during the First World War, often running into No Man’s Land to carry wounded soldiers to safety or to try to comfort those who were fatally injured.
The priest volunteered to be a military chaplain for the Irish division of the British Army after the war had been ongoing for over a year.
He served for around two years until his death at the Battle of Passchendaele on August 16, 1917.
Doyle was killed by shellfire while running to help two wounded soldiers, one of whom was from Belfast.
As the soldiers he was aiding were Protestant, the Catholic Church in Ireland has said that Doyle is an "ecumenical martyr of charity" for dying while helping soldiers of other Christian denominations.
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The sainthood campaign is being led by a Dublin-based group called the Fr Willie Doyle Association, which is supported by the clergy.
The group was founded by Patrick Kenny, a business school lecturer who lives not far from where Doyle grew up in Dalkey.
Kenny told the BBC: "Fr Willie Doyle lived a life of great heroism and, I would also say, great holiness.
"He was awarded the Military Cross for his bravery at the Battle of the Somme. He was mentioned in dispatches on a number of occasions as well."
He also said that the commander of Doyle’s division, which he joined in his early 40s, described the priest as "the bravest man that he ever met".
Kenny added that Doyle was also noted for his kindness and mercy towards injured German prisoners of war.
* This article was originally published on Extra.ie.