Around three hundred Fianna Fail members are eligible to vote at the convention to fill the seat on Donegal County Council held by the late Councillor Sean McEniff.
The long-serving Fianna Fail councillor from Bundoran passed away in April.
At one point it looked as though his daughter Elizabeth McIntyre would go forward uncontested but in recent weeks this has proved not to be the case.
Many in the Bundoran area hope the seat can stay locally in the town, however, the other candidates in the race now make that prospect much more difficult.
Former Ballyshannon Town Councillor Billy Grimes is also contesting the seat as is Roger Meehan from Dunkineely and Michael Naughton of Laghey.
The convention will take place at the Millpark Hotel in Donegal town on Sunday from 6pm.