Interim chief executive Charlie Adan, who arrived in January, has stepped down from the role.
Kate Josephs will become the new chief executive on a permanent contract but doesn't start until January.
Until then, the council will be run by John Macilwraith, executive director for people services, and Eugene Walker, executive director for resources.
Council Leader Julie Dore was due to step down in May's local elections but ended up carrying on when the coronavirus pandemic hit and the elections were cancelled.
Coun Dore and senior officers currently have special powers to make decisions under emergency Covid-19 legislation.
Pending CEO Kate Josephs began her career as a policy advisor in the Department for Work and Pensions. As a senior leader in the UK civil service, she held deputy director positions in HM Treasury and the Prime Minister’s Delivery Unit.