Jan Sobieraj, who has been in charge of the trust for four years, is set to retire following a major shakeup of the health service in the county.
ULHT confirmed that Mr Sobieraj will leave at the end of June, but no interim appointment has been made.
The trust announced in October 2018 that Mr Sobieraj had decided to retire.
Mr Sobieraj did not wish to comment on his departure at this stage.
Recruitment for a new chief executive is underway with interviews expected to take place the week commencing April 29.
Martin Rayson, director of human resources and organisational development, said: “The advert and process to recruit for a new chief executive at United Lincolnshire Hospitals NHS Trust is underway and will include consideration of any temporary appointments as well as longer term requirements.”
The news comes as the trust remains in special measures after been ranked inadequate by health inspectors and has run up an end of year deficit of £88.2 million.
During his time in charge, the trust has failed to hit its waiting time targets for A&E and cancer care for five years.
Meanwhile, ULHT continues to grapple with staffing shortages and has seen Grantham A&E downgraded to an urgent treatment centre under healthcare shakeup plans.