Chief Constable Martin Richards said that he planned to retire next year after more than six years in charge of Sussex Police.
Mr Richards, who joined the police 32 years ago, said: “This is not a decision I have taken lightly.
“My career as a police officer has been a rewarding one and it has been a particular privilege to serve as Chief Constable of Sussex.
“It had always been my intention to retire as is usual after 30 years’ service but I felt it right to support first the police authority in their final months and then the newly elected police and crime commissioner into her second year in office.
“It has been my good fortune to serve alongside excellent people and talented and committed partners who, together, have made a huge contribution towards consistently reducing crime in Sussex.
“I shall remember with affection and admiration a workforce that consistently demonstrates the highest qualities of compassion, courage, a sense of justice and above all an overwhelming desire to serve.”
Mr Richards plans to retire in March. He joined the force from Wiltshire where he also served as chief constable.
Police and crime commissioner Katy Bourne said: “I would like to recognise Martin’s tremendous contribution to Sussex Police during his six years as chief constable.
“It has been a pleasure working with him during my first year in office and he has been a great support to me.
“During his service as chief constable he has steered the force through difficult times and met some significant financial challenges.
“Plans are being put in place to advertise and recruit a new chief constable and in the meantime I have every confidence that the current chief officer team has the skills and resilience to lead the force.”