Beverley Flynn has announced tonight that she will not be contesting the next General Election.
The decision by the Fianna Fáil TD has caused widespread surprise in Co Mayo.
She is understood to be stepping down for family reasons.
Taoiseach Brian Cowen has said he wanted to thank Beverley Flynn for her commitment to politics and for her efforts on behalf of the Fianna Fáil Party.
He added that Ms Flynn is a very able politician and she has represented the people of Mayo with undoubted tenacity and skill in her time in Dáil Éireann.
Mr Cowen said that Beverley Flynn had been assiduous in her attention to the needs of her constituents and that her many supporters will be sorry to see her leave representative politics, while respecting her decision.
Meanwhile, the Minister of State for Labour Affairs, Dara Calleary, has paid tribute to his constituency colleague.
Dara Calleary said: 'Beverley has worked hard on behalf of the people of Mayo since she was first elected to Dáil Éireann in 1997.
'She has made a strong contribution to Irish politics and has been particularly committed to the area of health policy.'