Patricia King is to step down as the General Secretary of the Irish Congress of Trade Unions (ICTU) after seven years in the role.
She told members of ICTU's Executive Council of her decision at a meeting this morning and informed ICTU staff this afternoon.
Ms King is expected to remain in the position for the next few weeks until a successor has been appointed.
A recruitment process to fill the role is due to begin in the coming days.
Ms King took up the position of ICTU General Secretary in 2015 becoming the first woman to serve in the role.
She is a former vice-president of SIPTU and also served as one of two vice-presidents of ICTU.
Ms King was a full time official with SIPTU for over 25 years and became the first woman to serve as a national officer of the union when she was appointed vice-president, in May 2010.
She has represented workers in both the public and private sectors and was a lead negotiator in both the Croke Park and Haddington Road agreements.
Ms King played a leading role in the Irish Ferries dispute in 2005 and in subsequent negotiations that saw an overhaul of employment rights law and the establishment of the National Employment Rights Authority (NERA).
