The PSNI chief constable said he had been “hugely challenged” by the role as he prepares to step aside later this year.
George Hamilton is nearing the end of his five-year term.
He served 29 years in lower ranks before his current appointment.
Mr Hamilton said: “It has been an immense honour to have held this position, I have thoroughly enjoyed it, but I am not pretending otherwise, it has been hugely challenging.
“I just felt that at the end of the five year contribution, the most challenging role, it was time for me to think of doing other things.”
Mr Hamilton announced his departure amid continuing uncertainty over Brexit.
He appeared before the Policing Board on Thursday, its first meeting for two years following the collapse of Stormont devolution.
Board chair Anne Connolly said the appointment of a new chief constable and the timescales for bringing permanency to several senior vacancies that have arisen over the past two years has been given extensive consideration by the Board.
She added: “The Board has agreed that the chief constable appointment should take immediate priority.
“Other positions that are currently filled on a temporary basis will be scheduled in, but the Board also requires time to consider the future requisite structure and configuration of the service executive team.
She said: “Given the seniority of the position and the significant transformational change programme and challenges that the PSNI will face over the next five years, the appointment process will necessarily be robust whilst ensuring the most suitable candidate, based on merit principles, is selected.”
The Board plans to have the appointment process for the Chief Constable completed by the end of June 2019.
The chief constable, at the request of the Board, has been asked to consider a short extension of his tenure, if required, to ensure continuity in the leadership of the PSNI and the appointment of his successor.