'Rise' will be the name of TD Paul Murphy's new political party, which was launched this afternoon.
It stands for 'radical, internationalist, socialist and environmentalist’, and was formed after a split in the Socialist Party.
Mr Murphy is the group's only elected official and says he will stay within the Solidarity - People Before Profit banner in the Dáil.
Deputy Murphy acknowledges some people will see it as the left fracturing again.
He said: "I will understand people thinking that, to people who are a distance from the left, these debates may seem a bit obscure, I understand that.
"I think watch what we say, watch what we do, let things play out over a number of months and I think the differences in strategy will become clear to people."
Deputy Murphy said that he wants to build a broader left in Ireland.
"We are modest about what Rise is, Rise is not the new broad left that is needed in this country."
He said that the party is "a definite, distinct Marxist trend that seeks to contribute to the building of such a broader left".