It is the latest milestone in the recent official recognition of Irish citizens who fought in the wars, who for decades were forgotten, pilloried and blacklisted for joining the British armed forces.
The memorial to as many as 60,000 Irishmen and women killed in combat stands in Dublin's Glasnevin Cemetery, the country's largest burial ground and resting place to many of the state's founding fathers.
Just two years ago, the Irish Government apologised for the treatment of 4,500 Irishmen branded deserters for signing up to the fight against Nazi Germany during the Second World War.
The Cross of Sacrifice is erected in cemeteries around the world holding the graves of 40 or more war dead.
Ireland was the only such country not to have one.
It is important that the First World War, and those whose lives it claimed, be not left as a blank space in Irish history.
President Michael D Higgins
President Higgins said: "Today is a significant day, as we dedicate this Cross of Sacrifice - the first such Cross to be erected in the Republic of Ireland.
"On an occasion such as this we eliminate all the barriers that have stood between those Irish soldiers whose lives were taken in the war, whose remains for which we have responsibility, and whose memories we have a duty to respect.
"We cannot give back their lives to the dead, nor whole bodies to those who were wounded, or repair the grief, undo the disrespect that was sometimes shown to those who fought or their families.
"But we honour them all now, even if at a distance, and we do not ask, nor would it be appropriate to interrogate, their reasons for enlisting.
"If they could come back no doubt they would have questions to ask as to why it was, and how it came to be that their lives were taken."
The duke said it was an important step in the continuing process of remembering those who died.
"This represents a lasting tribute to their sacrifice and it is my hope, in the years to come, that memorials such as these continue to inspire successive generations to remember," he said.
We are extremely grateful to the Irish Government, public and the Glasnevin Trust, all of whom have done so much to support our work of commemoration and remembrance in Ireland.
Commonwealth War Graves Commission
There are more than 200 fallen soldiers from the world wars buried in Glasnevin alone and over 3,000 laid to rest or commemorated at 670 locations throughout the Republic.
The majority were casualties who died in the UK and were taken home for burial by their families.
But there are also many who were killed in ships torpedoed and sunk in the Second World War and whose bodies were washed ashore.
Deirdre Mills, director of UK operations with the Commonwealth War Graves Commission (CWGC), said she was delighted the landmark commemoration coincides with the centenary of the First World War.
She added: "The cross is an important feature of our work worldwide, commemorating those from both Ireland and throughout the Commonwealth who gave their lives during both world wars."
It is estimated around 210,000 Irishmen served in the British forces during the First World War, with many Irish descendants serving with other allied forces.
As many as 50,000 Irishmen died in the war.
In the Second World War, up to 100,000 Irishmen served and some 10,000 were killed.
Around 1,000 civilians were killed during air raids.
The Cross of Sacrifice was originally designed by renowned architect Sir Reginald Blomfield.
It represents the faith of the majority and the human sacrifice of all Commonwealth war dead, according to CWGC, which maintains the graves of 1.7 million servicemen and women who died in the conflicts.