The Law Reform Commission has recommended that a range of legal rights should be extended to couples who live together but are not married.
In a consultation paper published today, the LRC also calls for gay relationships to be recognised.
Speaking on RTÉ radio, the director of research at the LRC, Raymond Byrne, said that heterosexual and homosexual couples who are in long-term, marriage-like relationships are not recognised as such under the law.
The LRC proposes giving them rights and protections in areas including property affairs, succession rights, maintenance, pensions and tax.
The paper defines qualifying couples as those who have been living together for three years, or for two years where there is a child in the relationship.
More than 77,000 families were listed in the last census as cohabiting, and 1,300 were in same-sex relationships.