Babies made from two women and one man have been approved by the UK’s fertility regulator.
The historic and controversial move is to prevent children being born with deadly genetic diseases.
Doctors in Newcastle – who developed the advanced form of IVF – are expected to be the first to offer the procedure and have already appealed for donor eggs.
The first such child could be born, at the earliest, by the end of 2017.
Some families have lost multiple children to incurable mitochondrial diseases, which can leave people with insufficient energy to keep their heart beating.
The diseases are passed down from only the mother so a technique using a donor egg as well as the mother’s egg and father’s sperm has been developed.
The resulting child has a tiny amount of their DNA from the donor, but the procedure is legal, ethical and scientifically ready.
”It is a decision of historic importance,” said Sally Cheshire, chairwoman of the Human Fertilisation and Embryology Authority (HFEA).
”This is about cautious go ahead, not gung-ho go ahead, and there is a long way to go.
”I’m sure patients will be really pleased by what we’ve decided today.”
But some scientists have questioned the ethics of the technique, saying it could open the door to genetically-modified ’designer’ babies.
The HFEA must approve every clinic and every patient before the procedure can take place.
Three-person babies have been allowed only in cases where the risk of a child developing mitochondrial disease is very high.
Clinics can now apply to the HFEA for a licence to conduct three-person IVF.
However, the UK will not be the first country in the world to have children born through the three-person technique.
A Jordanian couple and doctors in New York performed the procedure in Mexico and the resulting baby is understood to be healthy.