South Tipperary TD Mattie McGrath claims he was forced into leaving Fianna Fail after being "double-crossed" by Finance Minister Brian Lenihan.
Announcing his decision to stand as an independent in the General Election, Mr McGrath said the party seemed to be protecting the rich and crucifying everyone else.
In a scathing attack on the leadership, he said Taoiseach Brian Cowen snubbed him while Mr Lenihan reneged on a deal they struck over bankers' bonuses and social welfare cuts.
"I felt I was let down and double-crossed," he said.
On Mr Cowen, he said: "He didn't engage and he never accepted me as the elected representative for South Tipperary because he had other cronies that he was dealing with, and that was his downfall, probably."
Mr McGrath joined Fianna Fail in 1975 at the age of just 16, following in the footsteps of his father James McGrath, who was a founder member.
He was first elected to the Dail in May 2007 and was formerly a councillor in South Tipperary County Council from 1999.
Mr McGrath was expelled from the parliamentary party last June for voting against the Government on the Wildlife (Amendment) Bill 2010, which banned stag hunting with dogs.
But he denied he was cynically resigning from the party now to save his own Dail seat, adding he had run out of "final straws" with Fianna Fail.
In particular, he pointed to unemployment, pay cuts, negative equity, the recent price hike at State-owned health insurer VHI and last week's political debacle for forcing his hand.
Sixteen other Fianna Fail TDs have already announced they will not contest the general election.
Referring to junior coalition partners the Green Party, Mr McGrath said "the tail was wagging the dogs".
"The events of last week really brought shame to many, many Fianna Fail people, and my father was a founding member of the party," said Mr McGrath.
"They let us down and let the country down, and that's the biggest issue."
He added: "We seem to be protecting the rich all the time and crucifying the ordinary people, the working man, the small farmer, the small business."
Mr McGrath said, if elected as an independent, he would consider forming a pact among centre-right candidates.
He said there was room for a new grouping that could support the new government.
WHAT a bitter end for Brian Cowen. It was his insistence on exercising his (perfectly legal, but politically inadvisable) Taoiseach's prerogative to reshuffle his Cabinet that hastened the inglorious end of his Government.