Sinn Fein TD for Louth Arthur Morgan has announced that he will not be standing for re-election at the next general election.
Mr Morgan said he would be stepping down to help run his family business.
He added that he would remain active in the party and would work to ensure a Sinn Fein successor in his seat.
Mr Morgan was elected to Louth County Council in June 1999 before he won a seat in the Dail in the 2002 general election, which he retained in 2007.
He is a member of the Foyle, Carlingford and Irish Lights Commission established under the Good Friday Agreement.
Speaking on Irish state broadcaster RTE, Mr Morgan said it was well known that he was reluctant to go into the Dail in the first place.
He added that Sinn Fein's leadership had accepted his decision and it had not caused a rift in the party.