Fine Gael front bench member, Mr Ivan Yates, is to announce his retirement from politics tomorrow or even today in the wake of the ousting of the party leader Mr John Bruton.
Reliable party sources said last night that Mr Yates, a Dail deputy for 20 years, had told close supporters and members of his family at the weekend that he would not contest the next general election.
He has represented the Wexford constituency since 1981.
Mr Yates (41) said last year he would retire from politics before the age of 50.
He was expected to contest the next general election and to serve in cabinet, should Fine Gael be returned to power.
However, his plans to leave politics have been accelerated following Mr Bruton's defeat. Mr Yates was a key figure in Mr Bruton's campaign to defend his leadership which failed narrowly by 39 votes to 33.
Mr Yates, minister for agriculture from 1994 to 1997, was one of Mr Bruton's most trusted supporters and defended him throughout his various difficulties as party leader.
He performed a similar role as a close associate of Mr Alan Dukes during his period as leader from 1987 to 1990.
Mr Yates could have reasonably expected to be appointed to the party front bench no matter who won next Friday's leadership contest.
He could also have expected to have been appointed to cabinet by a future Fine Gael taoiseach.
He could not be contacted for comment last night on the reasons for his decision.
However, he has spoken in the past of the pressures of balancing a demanding political career with involvement in a family business - a chain of betting shops - as well as family life.
He was deeply disappointed by Mr Bruton's defeat last week and announced immediately afterwards he would not serve on the next front bench no matter who became leader.
He also said he would not participate in any of the leadership campaigns and has not disclosed for whom he would be voting in that contest.
Mr Yates's decision will cause Fine Gael significant difficulties in Wexford where it once held three out of five seats.
Former TD and now Senator and MEP Ms Avril Doyle is unlikely to contest the general election.
This will leave Mr Michael D'Arcy as the sole sitting deputy on the Fine Gael ticket.