Cllr Lin Hazell succeeds Angela Macpherson, who stepped down earlier this month, following a damning Ofsted report which rated children’s services in the county as inadequate.
Ms Hazell was in charge of children’s services between 2005 and 2011, when the department was graded good by Ofsted on three occasions.
She will take up her new role on December 1, the same day as David Johnston takes over as the new managing director of children’s social care and learning.
Council leader Martin Tett said: “Lin’s commitment and experience will be vital in delivering the comprehensive improvement plan we set out following our Ofsted inspection report.
“She will be a real asset to the cabinet and her previous knowledge means she can hit the ground running.”
Ms Hazell said: “I am delighted to accept the appointment.
“We have a huge task ahead of us, but I am confident that we have a strong basis on which to move forward.
“I am looking forward to working with all children’s services staff to successfully deliver the improvements we have set out in our action plan.”