The Prime Minister will use a speech to admit that parents and children are too often overlooked and sometimes left worse off by reforms.
Their interests will from October become one of the formal elements of Whitehall impact assessments - alongside issues such as cost-effectiveness, equality and the environment.
"For someone from my political viewpoint who believes in building a stronger society from the bottom up, there is no better place to start than with family," the PM is expected to say today.
"So I think it's absolutely right that Government should do everything possible to help support and strengthen family life in Britain today.
"I want every government department to be held to account for the impact of their policies on the family."
He will say that the "reality" was that in the past the family "just hasn't been central to the way government thinks".
"So you get a whole load of policy decisions which take no account of the family and sometimes make these things worse," he will say.
"Whether it's the benefits system incentivising couples to live apart or penalising those who go out to work or whether it's excessive bureaucracy preventing loving couples from adopting children with no family at all.
"We can't go on having government taking decisions like this which ignore the impact on the family."
The Prime Minister will say that family and politics were "inextricably linked" and once the new test is introduced, any policies that fail to support family life will not be allowed to proceed.
"I said previously that we would introduce a family test into government," Mr Cameron will say.
"Now that test is being formalised as part of the impact assessment for all domestic policies.
"Put simply that means every single domestic policy that government comes up with will be examined for its impact on the family."