The Northern Ireland Prison Service is an executive agency of the Department of Justice, the headquarters of which are in Dundonald House in the Stormont Estate in Belfast.

It was established as an agency on 1 April 1995. Agency status was re-confirmed following a quinquennial review in 2000. The Prison Service is responsible for providing prison services in Northern Ireland. Its main statutory duties are set out in the Prison Act (Northern Ireland) 1953 and rules made under the Act.

The Prison Service is a major component of the wider criminal justice system and contributes alongside other partners, to achieving the system's overall aims and objectives. As the responsible Minister, the Secretary of State accounts to Parliament for the Prison Service and shares Ministerial responsibility and accountability for the criminal justice system as a whole with the Lord Chancellor and the Attorney General. The Prison Service is headed by the Director General. As of August 2009, the Northern Ireland Prison Service employed 1,893 staff.

The Prison Service currently has three operational establishments:

HMP Maghaberry: a modern high-security prison housing adult male long-term sentenced and remand prisoners, in both separated and integrated conditions. Immigration detainees are accommodated in the prison's Belfast facility.

HMP Magilligan - a medium-security prison housing shorter-term adult male prisoners which also has low-security accommodation for selected prisoners nearing the end of their sentences;

HM Prison and Young Offenders' Centre, HMP Hydebank Wood - a medium-to-low-security establishment accommodating male young offenders and all female prisoners (including female immigration detainees).

There is also a staff training facility, the Prison Service College, at Millisle, Co Down.