Ben Kernighan, chief executive of the National Union of Students, has left his job after less than 10 months in post.
In a statement, the NUS said that Kernighan had "decided he does not wish to continue in his position as chief executive and has now left the organisation".
Kernighan joined the NUS as chief executive in July after 15 years at the National Council for Voluntary Organisations, the last seven as deputy chief executive.
The NUS statement paid tribute to Kernighan’s achievements and said he led the complex process of bringing together disparate parts of the organisation under one new set of terms and conditions.
The student body said Kernighan had also helped to achieve policy successes around higher and further education funding and had won concessions on the lobbying act.
The NUS said its membership base grew under Kernighan’s leadership and that he oversaw the successful launch of the National Society for Apprentices.
"He used his wide network of contacts within civil society to broaden the reach and message of the NUS and place it in a strong position in the run-up to the general election," the statement said. "The organisation is grateful for Ben’s contribution and would like to take this opportunity to thank him and to wish him every success in the future."
Peter Robertson, managing director of NUS Services Ltd, the commercial arm of the union, will lead the NUS until a replacement chief executive is found.
On his Twitter profile, Kernighan describes himself as "freelance".