Details of major reforming family law described as the most important in the history of the state will be published later this week.

Taoiseach (Prime Minister) Enda Kenny said on Tuesday as Cabinet members prepared to discuss the wording of the bill that it’s “the most important change in family legislation since the foundation of the state.”

Minister for Public Expenditure and Reform Brendan Howlin said the legislation would deal with complex issues that would affect every household in the state.

The new law, when passed after promised lengthy discussion, will enable civil partners and cohabiting couples who have lived together for three years to jointly apply to adopt. That is something they cannot currently do as a couple – only individually.

If a spouse or partner has lived with a parent for three years and looked after the child for two years, they will be able to apply for guardianship or custody.

The legislation will allow a relative of the child to apply for custody if they have looked after them for 12 months, where no guardian is able or willing to do so.

Unmarried fathers will be given automatic guardianship rights if they have lived with their child’s mother continuously for a year, including three months after the birth.

The bill also provides for the establishment of a register where all children who are born via assisted human reproduction will be able to trace their donors.

Justice Minister Frances Fitzgerald was given clearance by the cabinet on Tuesday for the Children and Family Relations Bill – the biggest overhaul of child and parenting law in the history of the state.

Separately, Health Minister Leo Varadkar was preparing for the coalition government to take the first steps towards framing a new law on surrogate motherhood.

The issue of surrogacy was originally to be included in the Children and Family Relations Bill. But it was removed by Fitzgerald and passed on to Varadkar and his health department.

Varadkar is now drafting a general outline for what is called the Bill for Assisted Human Reproduction and Stem Cell research.

Ministers are addressing the complicated area of assisted human reproduction, surrogacy and in vitro fertilization (IVF) for the first time. They propose to regulate areas including surrogacy, embryo donation, the screening of embryos for serious genetic diseases or for sperm and egg donation, and research in this area.

The Children and Family Relationships Bill is seen as an effort by the government to remove the issue of children from the forthcoming same-sex referendum in May.

But it is uncertain whether the Bill for Assisted Human Reproduction and Stem Cell Research will be completed in the lifetime of the government which ends in April 2016 at latest.

Minister for Justice Frances Fitzgerald announces details of the new bill on Tuesday in Dublin.Photocall