The Secretary-General of the Department of Justice Noel Waters is to step down next February.
A statement from the department says he notified the Justice Minister Charlie Flanagan of his decision on Monday.
The department adds that he will have shortly served for 40 years, and that "this was noted as a matter of routine at today's Government meeting".
Mr Waters has been a public servant all his career, and served as director-general of the Irish Naturalisation and Immigration Service from 2010 to 2014.
In previous positions he led Corporate Affairs and the Reception and Integration Agency - and also worked in the minister's office and the immigration, prisons and garda divisions.
He had been the department's Accounting Officer and acting secretary-general since October 6th 2014.
Mr Waters took over from Brian Purcell, who left the position in 2014.
The secretary-general is the senior civil servant and non-political head of the department.
His job is day-to-day management and non-political strategic planning and direction.
He is responsible for safeguarding the funds under the control of the department, and ensuring the efficiency in the running of the department.
Labour TD Alan Kelly has criticised the latest developments.
Speaking on The Hard Shoulder here on Newstalk, Mr Kelly said the Government should have been more transparent over the events.
"One of the questions which I've down for answer this week is 'Does Charlie Flanagan actually have confidence in him (Noel Waters)?
"So now he won't have to answer that, probably."
"The fact is I don't believe that he had any intention of retiring up until recently.
"It's quite ironic that the Taoiseach of this country went in and prevaricated in relation to many of his answers today and didn't tell us that the Government had been informed today that the secretary-general was to retire".
Also referring to the O'Higgins Commission, which was set up following allegations made by Sergeant Maurice McCabe, Mr Kelly said: "Bottom line here: I do not have confidence in the Department of Justice.
"I've had enough experience now of the Department of Justice save quite frankly, as a former government minister who served not so long ago, I have no faith in the Department of Justice".