Dublin South-West TD Paul Murphy has officially announced that he is joining People Before Profit.
At a press briefing, Deputy Murphy said his party, RISE, would join forces with PBP and together they would build a "mass broad eco-socialist party".
Paul Murphy, who will now be designated as a People Before Profit TD, said the "left is coming together" and that he can "guarantee" that he will contest the next General Election as a PBP TD.
He said that both RISE and People Before Profit had worked closely together over the past number of months, particularly on calls for Ireland to pursue a "Zero Covid" strategy.
Richard Boyd Barrett welcomed Paul Murphy to the party and said PBP has seen an increase in membership in recent times, with "about 50 to 100 people joining every single month for pretty much the last year".
He said the party now had around 3,000 members.
Asked if People Before Profit would consider joining forces with Solidarity and become one party, Deputy Boyd Barrett said: "I think there's a lot of common ground, but they do differ with us on the question of a border poll."
He added that his party wanted to see the "ending [of] partition, uniting people for a different type of Ireland north and south is seriously on the agenda".