Miss Justice Mary Laffoy has announced her decision to resign as Chairperson of the Commission to Inquire into Child Abuse.
The announcement has been confirmed by the Department of Education.
A spokesperson declined to say if the resignation had been expected.
Miss Laffoy resigned in a letter to the Secretary General of the Government, Dermot McCarthy.
A statement on the Commission website states she has decided to resign as soon as a further Interim report is published in November.
No reason is given for the resignation.
The unexpected development comes just a day after the Government announced a further review of the Commission's remit.
A separate announcement on the website indicates that the work of the Commission's Investigation Committee is to be suspended, and no further hearings will take place until the Government's review is complete.
The Laffoy Commission was set up by the Government in May 1999 to address the effects of child abuse on its victims.
It has published two Interim Reports, in May and November of 2001.
Last December the Government began a review of its remit and yesterday the Education Minister, Noel Dempsey, announced a second phase of that process aimed at achieving the original intentions but within a more reasonable timeframe and in a cost effective manner.
Minister Dempsey said that the Commission would not complete its work for up to 11 years if it continued as currently established.
He also suggested that the current timeframe could mean legal fees of up to €200 million might be paid to persons against whom complaints had been made.