Until now, single fathers have always had to get the mother's blessing before they could be granted custody of their kids, a rule that fathers' organizations have long seen as unfairly weighted against them.
But now new legislation would allow unmarried fathers custody even if the mother is against it. The new law emphasizes that in normal circumstances both parents are to share responsibility for the child, unless this is not in the child's best interests.
Unmarried fathers denied joint custody of their children by mothers will in future be able to go to the Youth Welfare Office or appeal directly to the family court. The mother will then be given six weeks to give a statement on the father's custody application.
If the court does not see any threat to the child's interests, it will automatically grant the father custody on principle.
It would no longer be enough for the mother to say that she does not want any contact with the father, as the child's interests alone will now be prioritized.
German Justice Minister Sabine Leutheusser-Schnarrenberger said the new law was a clear step forward in social equality.
"Fathers will be in a much better position," she told Die Welt newspaper on Friday. The new custody rules would reflect social changes and the process would work "quickly and without bureaucracy," she added.
However, German fathers' organisations have said the new rules do not go far enough to redress the balance between parents.
The reform implements a ruling by the German Federal Constitutional Court in 2010 which overturned the existing law that a father cannot get joint custody without the mother's permission, a rule the European Court for Human Rights had also criticised.