Fine Gael Donegal South East TD Dinny McGinley, who has represented the constituency for 25 years, has announced that he will not contest the general election.
Mr McGinley's decision comes just days before the party finally holds a selection convention in the constituency following the cancellation of a bid to hold it a fortnight ago.
"This has not been an easy decision, but I feel it is the right time to pass on the political torch," said Mr McGinley, who was elected on seven successive occasions.
He said he had made the decision after a week's holidays at Easter. "I'm 63 years of age, and I asked myself if I wanted to be in Leinster House when I was nearly 70 years of age."
His decision, taken in consultation with family members and some close political supporters, was "entirely of my own making, without any interference by anybody else", he told The Irish Times.
A recent, strongly-disputed opinion poll had claimed that Mr McGinley would face a strong battle to hold on to his seat from Sinn Féin's Pearse Doherty, with both allegedly enjoying 13 per cent support.
Rejecting the findings last night, Mr McGinley said Fine Gael had increased its support in the constituency in 2002 when it fell everywhere else. The party also enjoyed an increase in support in the local elections.
Last night FG leader Enda Kenny, who was told last week by Mr McGinley of his decision to retire, thanked him "for his huge contribution, not just to Fine Gael, but to politics in Ireland".
He added: "With Dinny McGinley's retirement the people of Donegal are losing a true political champion. Dinny is an exceptionally talented man who worked tirelessly for the people of Donegal."