Sinn Fein will not help either of Ireland's two main parties form a coalition government.
With final numbers in a heavily fractured Dail parliament not expected until Monday, Gerry Adams dismissed any idea that his party would support one of the traditionally dominant forces in Irish politics - Fine Gael and Fianna Fail.
"We aren't going to go in there (to government) and betray our electorate and betray the other people who need a progressive government," he said.
"We are not going to go in and prop up a regressive and negative old conservative government, whatever the particular party political complexion."
Mr Adams's rejection of what would be a left-right coalition maintains the position his party adopted during the lacklustre election campaign.
With support for establishment parties plunging to a near record low, prospects for a new coalition government are in deep disarray and weeks of protracted negotiations are on the cards.
Taoiseach Enda Kenny ruled out resigning or re-running the poll.
His Fine Gael party suffered a hammer blow, losing about 30 seats, while its Labour Party partner was humiliated by the prospect of retaining fewer than 10 seats.
The other stories of the vote are the revival of Fianna Fail, which led the country in economic collapse five years ago, and Sinn Fein, which has continued its steady growth in the Republic.
The fracturing of traditional centre-right politics suggested widespread disaffection with the once dominant forces and austerity - a mirror of the voter schism which has crippled parliaments in Spain, Portugal and Greece.
Mr Adams said: "You can always do better. I would love that we were going into government with a majority - that takes time. These other parties have more depth, have more structures, have more organisation, have more resources."
Predictions point to a remarkable electoral swing where the political powerhouses of Fianna Fail and Fine Gael will struggle to secure 50% of popular support for the first time in history.
Mr Kenny said his party would remain a large bloc in the new Dail parliament despite throwing away the largest majority it had ever secured.
"I'd like to think that it could be possible, given the final results, to be able to put a government together that could work through the many challenges we have," he said.
The clearest majority would come from Fine Gael and Fianna Fail setting aside their historical rivalries, borne out of the civil war and cemented over the last 90-odd years.
In a remarkable comeback after its near wipe-out at the last election, Fianna Fail could almost double its seats.
But the once-dominant party in Irish politics will remain a long way from its heyday majority, which tumbled with the economic crash it presided over nearly a decade ago.
Mounting disillusionment with mainstream parties opened an unprecedented opportunity for smaller parties and independents.
Sinn Fein will be the third largest party.
Among the battered coalition's biggest casualties were Alex White, Labour's outgoing minister for communications, energy and natural resources, and Alan Shatter, the former Fine Gael justice minister, who were both defeated in Dublin Rathdown.
Labour leader Joan Burton said she was not resigning but neither would she be in government.
Mark Mortell, the Taoiseach's closest adviser, said Ireland would have to review its "political system" once the outcome of its most uncertain election in recent times is decided.
"The only word I can use right now is deep disappointment," he said.
Fine Gael and Fianna Fail, both centre-right, have swapped power since the foundation of the state.
Such a "grand coalition" would break new ground in potentially handing the Dail a definitive left-right split for the first time in history.
More than 550 candidates fought in 40 constituencies to become one of 158 TDs - eight seats fewer than the 2011 election when Fine Gael and Labour took office promising a democratic revolution.
Parties will have until March 10 - when the Dail is scheduled to resume - to forge a power-sharing deal.