Mr Robinson had been chief executive at the council since October 2006
The chief executive of Stoke-on-Trent City Council is quitting the job amid uncertainty about what will happen with the authority's leadership.
Steve Robinson said he was leaving the job to take up a similar post at the new Cheshire West and Chester Council.
Stoke Central MP Mark Fisher said Mr Robinson's move could not come at a worse time.
The council is considering radical changes to its structure after it was strongly criticised by a commission.
The government commission reported in May that residents in the city were being "short-changed" because the present set-up, which saw decisions made by an elected mayor and the chief executive, was not working.
He could not have chosen a worse moment to resign, when there are so many very big issues facing our city
Mark Fisher, Stoke Central MP
Mr Fisher said he was "absolutely shocked" to hear Mr Robinson was leaving the post.
He said: "It leaves the city in an extraordinary and very, very unfortunate position.
"He could not have chosen a worse moment to resign, when there are so many very big issues facing our city."
Mr Fisher added he was concerned the city's elected mayor Mark Meredith, who is in his first term of power, was "too inexperienced" to make the decisions by himself.
The city's former elected mayor Mike Wolfe said it was "awful news" and said Mr Robinson should have stayed to see through the projects he had started.
Last week, councillors voted to set up a board to look at issues like reducing the number of councillors, reviewing their pay and expenses and how to raise the profile of the city.
Professor Mick Temple was on the debate panel
Residents are presently being consulted over whether the city should ditch the current system of electing a mayor and revert to installing a council leader with cabinet.
Mr Robinson, 52, who has been working as the chief executive since October 2006, will take up his new post on 1 October.
He said he was "very sad" to be leaving Stoke-on-Trent.
He added: "I believe I leave it extremely well placed for the future as the most improved council in the country.
"I have been offered a unique opportunity to lead a brand new council. This is a wonderful challenge for me personally but I shall miss my many friends and colleagues here in Stoke-on-Trent."
Mr Meredith said he had "achieved a great deal" with Mr Robinson.
Mr Meredith added: "I would like to pay tribute to Steve's focus, determination and leadership.
"He has earned the admiration of everyone he has dealt with, from staff to government ministers."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.