The change is part of Ireland’s new civil partnership laws, which give gay couples almost all the rights of marriage.
However, couples who wed in countries where gay marriage is legal will find their unions downgraded to civil partnerships.
And some unions, such as French PACS, will not be recognised because they are deemed not to offer as many rights as Irish marriages or civil partnerships.
Unions from 27 countries or states will be recognised; 17 of which currently give gay couples the right to marry. Couples will be automatically considered as civil partners and will not need to register.
Brian Sheehan of the Gay and Lesbian Equality Network said: “Same-sex couples who have already celebrated their relationships and made formal commitments to each other by having a civil marriage or civil partnership in another country will today have those relationships recognised in Ireland. This recognition will provide significant protections for these couples.”
The first Irish civil partnership ceremonies will take place in early April.