The referendum to introduce the 39th Amendment and change the constitutional definition of the Family has failed by an overwhelming 67.69%.
The amendment sought to change the wording of the family from being solely based on marriage to being based on “durable relationships”.
National turnout was 44.36% with a final result of Yes 32.31% and No 67.69%.
Early counting in the RDS and across Ireland quickly indicated that the referendum would not be passed.
Donegal had the highest No vote with 78.08% against the amendment.
Only Dún-Laoghaire voted in favour of the Family amendment, although it was by a razor-thin margin of 50.29%.
Dublin Mid-West voted No by the largest margin in the Dublin region at 80.21%.
Ahead of the full results being announced, Taoiseach Leo Varadkar said the Government “clearly got it wrong” in their campaign.
“It was our responsibility to convince the majority of people and we failed to do so,” he said.
“We struggled to convince people of the necessity or need of the referendum at all, let alone the details and the wording.
“That is something we’re obviously going to have to reflect on in the week and months ahead.”
Tánaiste Micheál Martin said the “result of the referendums on family and care is clear”.
“There is no single reason why these proposals were rejected and, like all who supported them, we will reflect on this over time,” he said.
“While the constitutional change was rejected, it is clear that the need for continued action to support families and to respect principles of equality was not challenged.”
Sinn Féin leader Mary Lou McDonald, who supported a 'Yes/Yes' vote, said the result was "a moment of reflection for the Government who went on a solo run".
One Family CEO Karen Kiernan said the organisation was "devastated".
“It is so disappointing that this opportunity to include unmarried and single parent families in our Constitution has been rejected by the Irish people,” she said.
“The fact that their heartfelt desire for their families to be included in the Constitution is no longer a reality in their lifetimes is a massive rejection to them.”
Those against the Family amendment said the phrase "durable relationships" could be defined by the courts, posing risk to family law, inheritance law and immigration law.
Additional reporting: Jack Quann
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