Councillor David McGuinness has been selected by Fianna Fail to contest the forthcoming by-election in Dublin West.
It follows the resignation of Independent TD Patrick Nulty after he admitted sending inappropriate social media messages to a teenage girl.
McGuinness defeated compeition from Edward Mcmanus, a local area representative for the party, and Anita Lenihan, the sister of the late Brian Lenihan.
The government is expected to move the writ for the election this week so that it can be held on the same day as the European and Local elections.
Mortgage debt campaigner David Hall is also contesting the by-election, as is Ruth Coppinger of the Socialist Party.