The Marriage Foundation says since 1980, the proportion of children born to married couples has fallen from 88% to 53%.
It says couples who were not married at the time of their child's birth are more than twice as likely to split up during the next 15 years, even if they subsequently married.
The research highlighted that other groups are contributing towards keeping the births within wedlock up. More than 80% of births to Pakistani and Indian mothers were to married parents.
It says an estimated 1.8 million additional children born since the 1980s are either are not living with both natural parents already or are likely to experience family breakdown.
The trend away from marriage since then has increased family breakdown in England and Wales by up to 44%.
Harry Benson is a Christian from the Marriage Foundation. He said it is the staying together of partners that makes a difference to children, whether they are married or not.
He told Premier's News Hour: "Mum's have got older when they're having babies - that ought to be good for family breakdown, wiser mums - less family breakdown - but that hasn't happened.
"Families are richer, disposable income's gone up by about double since 1980. And that should have been good for families but it hasn't been. Family breakdown's doubled.
"Then education's improved a lot since 1980 as well - GCSE pass rates for example." He said all of these things would point towards more secure family unit - however this has not happened.
Listen to Premier's Antony Bushfield speak with Harry Benson here:
