Fianna Fáil has selected Mayo GP Dr Keith Swanick as its candidate in the upcoming Seanad byelection.
Sinn Féin has also agreed to nominate a candidate.
The party decided at the weekend to contest the seat left vacant by Labour Senator Jimmy Harte, who retired after a long illness.
A spokesman for Sinn Féin said the Ard Chomhairle will be consulted on Thursday and the name will be confirmed after an agreement is secured.
Maíria Cahill is the Labour Party nominee for the seat. Ms Cahill is from a high-profile republican family.
Her great-uncle, Joe Cahill, was a founding member of the Provisional IRA.
A vocal critic of Sinn Féin, she came to public attention during a BBC Spotlight programme where she alleged sexual abuse by a senior IRA figure and later being subjected to a "kangaroo court" investigation by republicans.
She pursued the matter through the courts but then withdrew her evidence after losing faith in the the North’s Public Prosecution Service.
PPS director Barra McGrory subsequently apologised for its handling of the case.
Nominations close on Thursday and ballots are to be distributed to all members on October 30th.
A result will be declared on November 13th.
