Wicklow TD Liz McManus has declared she will not contest the Labour leadership race.
Ending speculation about her own candidacy, the acting party leader said she would support Dún Laoghaire TD Eamon Gilmore in his bid to succeed Pat Rabbitte.
Candidates for the leadership of the Labour Party have until next Thursday to throw their hats in the ring.
The party's national executive committee met in Dublin today and ruled a ballot would be held in one month's time with the new leader taking office on October 5th.
An estimated 4,000 party members, who have been fully paid up for the last two years, will be entitled to vote.
The executive decided nominations would officially open today and close next Thursday at noon. The election day will be October 4th with the new leader and deputy leader taking office October 5th.
Mr Gilmore, who is firm favourite to become the next leader, remains the only deputy to declare his candidacy for the post.
Pat Rabbitte resigned as leader last week following a disappointing general election in which the party failed to make the hoped-for breakthrough.
In a statement today, Ms McManus said she had been impressed by the energy and focus that Mr Gilmore was already bringing to the challenge.
"For these reasons and bearing in mind that the European elections are less than two years away and offer us new opportunities to grow the party I do not intend to contest these leadership election," she said.
Ms McManus also declared her support for Limerick East TD Jan O'Sullivan as deputy leader, whom she said would provide the "necessary balance for a powerful leadership team".
Along with Ms McManus's support, Mr Gilmore has also received the backing of former leader Ruairí Quinn and the current chief whip Emmet Stagg.
His chances were significantly boosted earlier this week when finance spokeswoman Joan Burton surprised colleagues by announcing she would not be contesting the leadership of the party, but will seek the deputy leadership instead.
Dublin North East's Tommy Broughan, the only other TD still considering entering the race, is also expected to announce his decision soon.
So far Ms Burton and Ms O'Sullivan are the only candidates to declare themselves interested in the deputy leadership post. Cork South Central TD Ciarán Lynch said he was also considering running for this position.
Earlier in the week, Wexford TD Brendan Howlin and Dublin North West TD Róisín Shortall both ruled themselves out of the leadership race.
