Marc MacSharry has resigned from Fianna Fáil following a row over the handling of a bullying complaint against him.
The Sligo-Leitrim TD issued a statement this morning confirming the move, and said he will continue to work as an Independent.
Mr MacSharry, who has long been an outspoken critic of Taoiseach Micheál Martin, is unhappy at how a complaint by a local Fiana Fáil councillor, Donal Gilroy, has been dealt with by the party leader.
The complaint relates to comments made in a private WhatsApp group setup by Mr MacSharry to communicate with Fianna Fáil councillors in his constituency.
Mr MacSharry said: "This complaint related to exchanges between us over several months on services I have secured for Sligo University Hospital and their significance.
"It was a robust issue and robust language was used.
"I will continue to work as an independent member of Dáil Éireann to the very best of my ability on behalf of my constituency and our community and the many challenges and opportunities we face.
"I wish to thank members of Fianna Fáil in Sligo, Leitrim, south Donegal, north Roscommon and beyond together with those in the Parliamentary Party who have provided their steadfast support in recent weeks and through the years."
In a letter to the Fianna Fáil party last month, Mr McSharry said: "It is not bullying to criticise other elected Fianna Fáil representatives.
"I have repeatedly been subjected to criticism by other Fianna Fáil representatives and I fully respect their entitlement to criticise me."
He added that the use of expletives in discussions with colleagues is not bullying and if it is "then political debate will be totally curtailed".
A spokesperson for Fianna Fáil and Mr Martin has said they "strongly reject the assertions made by Deputy MacSharry in relation to the written complaint received by the Party."
They added that Mr MacSharry's resignation has been received and they wish him well for the future.
Minister for Agriculture Charlie McConalogue said that he was surprised and disappointed at the resignation.
Speaking on RTÉ's Drivetime, Mr McConalogue said that he did not see Mr MacSharry's point on the Taoiseach’s handling of the complaint and did not agree with him.
He said that the party had acted appropriately in its approach and it should have been allowed the opportunity to be dealt with.