The Northern Ireland Prison Service has announced that Director General Sue McAllister will leave her post at the end of October.
Mrs McAllister was appointed in May 2012 and was the first woman to hold the most senior position within a prison service anywhere in the UK.
An open recruitment competition will be launched in September for her successor.
Justice Minister Claire Sugden said: “The role of Director General is a uniquely challenging post and Sue McAllister has led the organisation through the reforms, which have placed rehabilitation at the core of its work.
“The Prison Service plays a vital role in the justice system and Sue can be proud of what she has achieved in her time as Director General.”
Sue McAllister said: “It has been a great privilege to lead the Prison Service over the past four years. When I became Director General my focus was to lead the transformational reform envisaged in the Prison Review Report. With the conclusion of the reform programme in March, my role has come to a natural end and the time is right for a new Director General to lead the Service.”
Mrs McAllister paid tribute to the staff in the Northern Ireland Prison Service and in particular to the two officers murdered since 2012.
“The murders of David Black and Adrian Ismay were despicable and an attack on the whole community. Both came as a tremendous shock and I want to pay tribute to their families, friends and colleagues.
“Working in prisons in Northern Ireland is different and I have always been hugely impressed by the courage, professionalism and dedication of my colleagues. They play a crucial part in making Northern Ireland a safer place and I want to thank them all for their hard work over the last four years.”