Minister for Justice Frances Fitzgerald will today brief Opposition spokespeople on major legislation to change the concepts of guardianship and parentage which will also play an important part in the debate on the same-sex marriage referendum.

Ms Fitzgerald will bring the Children and Family Relationship Bill to next Tuesday’s Cabinet meeting ahead of its publication later that day.

The 90-section Bill represents a substantial reform of how the family is defined and will give new guardianship rights to unmarried fathers, to same-sex partners and wider family members.

It will also allow civil-partnered or cohabiting couples to be eligible jointly to adopt a child. This provision will allow same-sex couples to adopt jointly for the first time – until now, the right to adopt extended only to a single person who was not married.

The Bill does not substantially differ from the general scheme (draft) that was published in September.

The legislation will establish in law the concept that the best interests of the child are paramount in decisions on custody, guardianship and access.

Unmarried fathers who have lived with the child’s mother for at least 12 months, including three months following the child’s birth, will be entitled to have guardianship rights. This makes it easier for the father to acquire custody rights.

It will allow civil partners, step-parents, those cohabiting with the biological parent and those acting in loco parentis for a specified period to apply for guardianship and custody.

In addition, members of the wider family will be allowed apply for the first time for access to the child.

The scheme announced by Ms Fitzgerald last September differed from the scheme published by her predecessor, Alan Shatter.

He included provisions in relation to surrogacy but they have since been removed and are now being dealt with by separate legislation being drafted by Minister for Health Leo Varadkar.

And following the recommendation of the all-party committee on justice, a child conceived through a donor or through assisted reproduction will have the right to trace his or her identity.