Éamon Ó Cuív has resigned as the Fianna Fáil deputy leader and spokesperson on communications after differences with party leader Michael Martin over the EU fiscal treaty.
He handed in his resignation this afternoon to party leader Micheál Martin who accepted it.
Mr Martin said: "Éamon's refusal to support the Parliamentary Party's position on the Fiscal Compact meant that it was no longer feasible for him to occupy these roles.
"As the party prepares for a momentous Ard Fheis this weekend, it is my hope that Éamon will continue to work for Fianna Fáil's renewal as he has done over the last twelve months.
"Our Party has led Ireland's positive and constructive engagement with Europe for generations and I am determined that it continues in this proud tradition."
Deputy O'Cuiv has said he will attend the Fianna Fáil Ard Fheis this weekend.