Independent Senator Martin McAleese has told Seanad Cathaoirleach Paddy Burke he will be resigning from the Seanad next week.
The husband of former President Mary McAleese was appointed as one of Taoiseach Enda Kenny's nominees.
He has recently completed a report on the Magdalene Laundries, which is due to be published next Tuesday.
Sources in the Taoiseach's office paid tribute to his work on the issue and on building bridges between Catholics and Protestants in Northern Ireland.
Senator McAleese was at the centre of efforts to bring loyalist paramilitaries in from the margins of the peace process.