The charities, which share a similar pro-family ethos, believe the merger will enable them to support even more families by opening up access to each other's resources and delivery models.
The merger proposal has been approved by the trustees of both charities and the legal and due diligence processes are now well underway.
Care for the Family said the two charities would be more effective in reaching families by working together rather than alone.
Mark Molden, Chief Executive of Care for the Family, said: "We are delighted that this merger is taking place. Positive Parenting brings with it a wealth of experience, quality resources and a training programme which will benefit parents across the UK.
"Our mutual desire is to see families strengthened and parents equipped in their vital role. This strategic merger will enable us both to see this develop over the years to come."
Around 8,000 parents attend parenting courses run by Positive Parenting, with its Time Out series currently being used by local authorities, schools, churches and children's centres.
More than 300,000 people have attended family-building events and training courses run by Care for the Family.
Ken Shorey, CEO of Positive Parenting, said: "This is a fantastic opportunity for both charities to expand their work.
"We are excited about the potential of this merger and the impact it will have in the long term for parents and families.
"Care for the Family is one of the key family charities today and we are delighted to be able to increase our capacity by drawing on their expertise and resources."
Care for the Family was founded in 1988 by best selling author and international speaker Rob Parsons. It aims to strengthen family life across the UK and help those facing family difficulties. It has over 100 staff with regional offices in Northern Ireland, Scotland, Isle of Man and Greater Manchester.
Positive Parenting was founded 35 years ago in Portsmouth. It has developed into one of the country's leading parenting charities, producing resources and providing training for parents and those who work with them. It has a staff of 14 with its head office in Birmingham and regional offices in Croydon, Birmingham, Rotherham and Scotland.
