Emma Harrison, head of welfare-to-work training company A4e, is to lead a pilot scheme in six to ten areas of the country.
Ms Harrison, who has more than 20 years' experience helping the long-term unemployed find jobs, will also take on the role of 'family champion'.
Speaking to the family guidance charity Relate, the Prime Minister said, 'What works is focused, personalised support, someone the family trusts coming into their home to help them improve their lives step-by-step, month-by-month. Emma Harrison understands that. She refuses to believe that some people are lost causes and has a proven track record of turning lives around.'
Mr Cameron also said the Government will consult on a system of flexible parental leave to let mothers and fathers share childcare during the first year of a child's life.
Children's minister Sarah Teather announced £30m funding over four years to help support family relationships by providing counselling and relationship support for couples, for example, through Sure Start Children's Centres.
The funding is aimed at preventative support and minimising the negative impacts for children when relationships break down.
Anne Longfield, chief executive of 4Children, said, 'As a result of our national consultation, The Family Commission, we called for more support for families and family relationships to be provided through Sure Start Children's Centres. We are delighted that the Government has listened to 4Children and to families.'
Local authorities will also be given new freedoms to pool their budgets to help support troubled families.