Platt will take up the role on September 1, subject to approval from the Financial Conduct Authority.
Current chief exec Turner will take up the role of non-executive chairman while David Watson will become deputy chairman and senior independent director.
Platt joins Countrywide following a 20-year stint at Bupa where she occupied a number of senior roles including managing director of its UK, Europe and North America business.
Most recently Platt was managing director of Bupa’s international development markets business and is currently a non-executive director of Cable & Wireless Communications.
“I am looking forward to working with our award-winning employees to provide a first class service to all our customers and helping the group become even more successful,” she said.
“I firmly believe that there are significant opportunities available for Countrywide as an integrated player to further strengthen its business and performance through the recovery of the UK property market.”
Grenville Turner said: “I am delighted to be welcoming Alison to the group and to be handing over responsibility to such a proven and energetic individual. In assuming the role of non-executive chairman I look forward to continuing to work with the board and supporting the new group chief executive through the next chapter of the group’s journey.”
