Verona Murphy is the frontrunner to be voted Ceann Comhairle for the incoming Dáil on Wednesday after both Fianna Fáil and Fine Gael backed the Independent TD.
At their respective parliamentary party meetings, Micheál Martin and Simon Harris proposed members support Ms Murphy's candidacy.
With Fine Gael and Fianna Fáil on a combined 86 seats, alongside the nine within the Regional Independent group, it is enough for Ms Murphy to be elected as Ceann Comhairle on the first count.
If elected on Wednesday, Ms Murphy would become the first female Ceann Comhairle in the history of the State.
Within Fine Gael, the recommendation from Mr Harris was widely accepted with one senior party source saying there will be "very few rebels" against voting for Ms Murphy in the secret ballot.
Mr Harris told the meeting that it was the right thing to do to ensure a new government can be formed in January.
Despite broad agreement in Fianna Fáil, John McGuinness and outgoing Ceann Comhairle Seán Ó Fearghaíl will remain in the race.
Mr Ó Fearghaíl was unequivocal in his criticism of the decision of Mr Martin to back an Independent candidate in an effort to support talks to form a government.
He said it was made clear in a conversation he had with Mr Martin last week that supporting Ms Murphy's bid was utmost on the agenda but at no point had he considered, nor was he asked, to withdraw from the race.
"We have done a lot to bring home to the people that Leinster House and the complex here belongs to the people," he said, expressing concern that this development will add to public cynicism surrounding politics.
He said that he is disappointed as someone who has worked for the past two terms to achieve "pretty radical reform" to see party leaders take a decision that is contrary to the reforms implemented to ensure the roles of Ceann Comhairle and Leas Ceann Comhairle would not be party politically biased.
Mr Ó Fearghaíl said that he "bitterly regrets" being persuaded to go forward for the role again after he had previously intended to return to the Fianna Fáil backbenches following the election.
The Social Democrats also criticised Fianna Fáil for opting to endorse a candidate despite a secret ballot being introduced to ensure TDs are free to vote for whomever they believed would be best in the role.
A spokesperson for the party called it extraordinary that Fianna Fáil would choose to endorse an Independent candidate despite two members of the party expressing their interest.
"There are now attempts to erode this progressive reform with two of the larger parties endorsing an Independent candidate," they said.
"It is clear that what is happening is a stitch up, by Fianna Fáil and Fine Gael, who are attempting to use the office of Ceann Comhairle as a bargaining chip in government formation talks."
Social Democrats will not be endorsing a candidate in light of what it said is a "regressive step" by Mr Martin and Mr Harris.
Meanwhile, it is expected that neither Fianna Fáil nor Fine Gael will endorse a candidate for Taoiseach on Wednesday as government formation talks continue. Sinn Féin will nominate Mary Lou McDonald for Taoiseach when the Dáil sits.