Nadine Peatfield, leader of the council, added: “I’m pleased to welcome Sam as interim chief executive.
“She has been a driving force for our neighbourhoods and a key leader in our resilience work.
“Together, we are committed to supporting our residents and staff as we navigate the Local Government Reorganisation process and lead the city forward into this next chapter.”
Simpson stepped down from the position earlier this month to take on a new role.
He joined the council in 1991 as a trainee accounting technician and returned in 2019 as strategic director of corporate resources and deputy chief executive.
Simpson said it had been a “huge privilege to serve my home city”, and he was “immensely proud” of what the authority had achieved together.