People Before Profit leader Richard Boyd Barrett has called on other left parties to form an alliance and rule out entering government with Fine Gael or Fianna Fáil.
The Dun Laoghaire TD was speaking after the final leaders debate, which saw Mary Lou McDonald, Micheál Martin and Simon Harris fail to land a final blow before Friday.
Mr Boyd Barrett said people would like an alternative to Fine Gael and Fianna Fáil, and says left-wing parties must present that to voters.
Speaking to Breakingnews.ie, Mr Boyd Barrett accused other parties of showing a lack of ambition.
"If a lot of people are looking for an alternative to 100 year or Fianna Fáil and Fine Gael, they have really got to believe in the alternative.
"That is why we have been pushing very hard the idea of a left alliance and a left government, setting that out clearly.
"Fianna Fáil and Fine Gael are on a historic decline, but the left have to prove that they have a viable alternative. That can only really convince people if the left make a clear push to band together and rule out future deals with Fianna Fáil and Fine Gael."
Mr Boyd Barrett said People Before Profit have contacted other parties on the left several times in recent years to form a left alliance.
However, he said they have got no response, and warned of previous governments that included the Labour and Green Party.
"There is a historic opportunity. There is no doubt about the historical trajectory of Fianna Fáil and Fine Gael being on the decline. They only have 40 per cent between them. That means 60 per cent of people are looking for an alternative.
"If the left want to take advantage of this historic opportunity and break the cycle of Fianna Fáil and Fine Gael, [the left parties] need to make an alliance, and need to rule out propping up Fianna Fáil and Fine Gael again, which has disastrous consequences in the past, most particularly for the Labour and the Green Party."
He said his party has sent emails to the others calling for such an alliance.
"We have got no response, and I think that shows a lack of ambition from other parties on the left. It is like they don't even believe in themselves enough, to believe that we can strike out break out of that cycle of Fine Gael and Fianna Fáil.
"If you keep open that option, what you are really telling the electorate is, you are not sure if there is an alternative to Fianna Fáil and Fine Gael."
In what could prove to be one of the most crucial moments of the election, the encounter between Simon Harris and disability worker Charlotte Fallon has dominated the headlines.
In a clip that dominated headlines, Ms Fallon tells the Taoiseach carers “were ignored” and the Government has “done nothing for us”.
Mr Harris responds by saying “no, not at all” and “that’s not true” several times before shaking her hand.
Mr Boyd Barrett said this showed "the veil has slipped" when it comes to the Taoiseach.
"Simon Harris has been an effective PR guy for the first few months of his rise to office of Taoiseach, but I think behind the PR, Fine Gael aren't the new energy, they are the same old politics that we have had for a long, long time.
"That, to my mind, is a politics of a small group of people who are disconnected from where the majority of working people are at, and the hardships they are suffering.
"I think that disconnected, and maybe even contempt or disrespect of the political establishment for ordinary working people and the real struggles they are going through, and for those who are vulnerable in our society, was badly exposed."
