Fianna Fáil Leader Micheál Martin has said he is receiving strong messages of support from party members in relation to the programme for government.
Speaking last night after his parliamentary party endorsed the document, Mr Martin said the overwhelming majority of those present had approved the decision.
He conceded that some people had "queries and clarifications", and others had "reservations" in terms of political strategy.
Mr Martin said the overwhelming majority were in favour of the content of the document and believed it had a significant "Fianna Fáil imprint".
Speaking at the Convention Centre in Dublin, he said he thought the "vast majority of the wider party would support the programme for government and would urge members in their constituencies to do likewise".
Asked about grassroots concerns about forming a government with Fine Gael, Mr Martin said he believed there was an obligation to do so.
He said "it was a challenge in any party, but from my perspective there is an obligation to the country".
He said there was a much more fragmented political system in the aftermath of the General Election and said that "we have to deal with that and be realistic about it".
Mr Martin said that in recent weeks he has had a "very professional" relationship with Fine Gael leader Leo Varadkar. He said he had never adopted a personal approach in his dealings with the Taoiseach.
Mr Martin said he was receiving very strong messages of support from across the country, from members of the party who believed it was "important that we go into government and that the country gets a government, particularly given the very serious challenges" that lie ahead.
He said there would now be a "vigorous debate" and that members would have their say in a postal vote.
Mr Martin said "TDs and senators wanted to go out and engage with the membership, to persuade members of the strength of this document, its relevancy to where people are today in their lives, and the need to get it passed and a government formed".
He described last night's meeting of the parliamentary party as "constructive with a very strong endorsement of the programme for government". He said many speakers had contributed on various aspects of the programme, particularly in relation to housing, agriculture and farming.
Mr Martin said there was also a "very strong endorsement of the investment into cycling, greenways and walking routes".
The parliamentary parties of Fianna Fáil, Fine Gael and the Greens endorsed the programme for government late last night.
The document will be now be posted to their individual memberships for ballot.
Green Party Deputy Leader Catherine Martin endorsed the plan, something regarded as significant in helping to secure the required two-thirds backing of party membership.
In a statement, she said Ireland was in the midst of a period of immense and unprecedented challenge, and stability and political certainty were needed.
The Dublin Rathdown TD said she was satisfied that the deal, which she helped to negotiate, was the best achievable one and it included some worthwhile and transformative policies.
Ms Martin added, however, that the Green Party's overriding concern if in government, would be the verifiable implementation of those policies.
However, only nine of the Green Party's 12 TDs backed the plan, with three other deputies abstaining in a vote.
The Green Party has informed its members how the parliamentary party voted last night.
Three TDs - Francis Noel Duffy, Patrick Costello and Neasa Hourigan - abstained in the vote, along with the Northern Ireland MLA Clare Bailey.
The other nine TDs, as well as their two senators and two MEPs, voted in favour of the plan.
The deal now goes to the party membership to decide whether or not to ratify the document, something which requires a two-thirds majority.
The first hustings will be a membership teleconference this Thursday night.
The results of the postal ballots will be known on 26 June.
The agreement came after weeks of negotiations between the parties and more than 120 days after the country went to the polls in February.
Under the programme, the office of Taoiseach is to be rotated between Micheál Martin and Leo Varadkar.
If it is ratified, Mr Martin would be elected Taoiseach before the end of the month and serve until December 2022.
Mr Martin described the deal as a "historic development" and denied his party was losing its identity by going into government with Fine Gael and the Green Party.
Mr Varadkar, who has continued as Taoiseach since the election, described it as "a good package overall", but acknowledged that borrowing would be needed to pay for many of the spending commitments.
Included in the document, which Minister for Finance Paschal Donohoe confirmed was uncosted, are proposals for major cuts to Ireland's greenhouse gas emissions, ending direct provision, caps on childcare fees, and increased supply of social housing.
Green Party leader Eamon Ryan said the programme for government was going to be "good for rural Ireland".
However, Sinn Féin has criticised the draft document as "aspirational" and "lacking clarity".
Party leader Mary Lou McDonald said many who voted in the general election for real change in housing and health would be disappointed.
Additional reporting: Paul Cunningham