The Irish National Liberation Army, the Official IRA and the loyalist south east Antrim brigade all announced they had disarmed just 24 hours before an amnesty for paramilitaries expires.
On Monday afternoon, Gordon Brown told the House of Commons that the south east Antrim brigade had destroyed its entire arsenal.
The breakaway faction of the UDA is the last remaining armed loyalist paramilitary group to decommission.
Mr Brown said this was a "central part of moving Northern Ireland from violence to peace".
Earlier, two republican paramilitary groups also confirmed they have destroyed their weapons.
The Irish National Liberation Army said it had disposed of its illegal arsenal in recent weeks through the Independent International Commission on Decommissioning.
The ruthless republican splinter group killed more than 100 people during the Troubles.
A spokesman for the INLA, Martin McMonagle, told a Belfast press conference:
"We make no apology for our part in the conflict," he said.
But he added: "We believe that conditions have now changed in such a way that other options are open to revolutionaries in order to pursue and ultimately achieve our objectives."
A prominent member of the INLA's political wing, and a former INLA prisoner, he said his group would now work to encourage political progress.
Hours later, the Official IRA, which is a relatively small organisation most active in the 1970s, also confirmed the move at a Belfast press conference.
In a statement, the group said:
"We have emphasised our commitment to removing any doubts that may exist that there are any Official IRA weapons in circulation.
"To this end an extensive nationwide inventory has been completed to confirm and verify that all such equipment has been located, identified and transferred to the decommissioning body. Any other such equipment, which has not been submitted to the decommissioning process, has no association with the Official IRA."
The Official IRA emerged at the start of the Troubles when the republican movement split into the Official and Provisional IRA.
The Official IRA declared a ceasefire in 1972, but later became involved in bitter republican feuds.
It is understood to have killed around 57 people.
The group said it had abandoned violence and indicated that public support for the Good Friday Agreement of 1998 and the wider peace process should be recognised.
The timing of the separate announcements is linked to the fact that the legislation which allows illegal groups to decommission weapons without fear of prosecution runs out on Tuesday.
Once the Independent International Commission on Decommissioning ceases to exist, any paramilitaries found in possession of weapons face prosecution and imprisonment.
Recovered arms will also be forensically tested to secure convictions.
Sinn Fein MLA Gerry Kelly has welcomed the INLA move.
He said: "The peace process has ensured that a peaceful and democratic path to a united Ireland exists. There is no support for or appetite for armed actions within the republican community."
"The INLA has recognised this by engaging with the IICD in this action."
The loyalist Ulster Political Research Group, linked to the paramilitary UDA which recently decommissioned its weapons, also welcomed the INLA announcement.
"We are sure we can speak for the widest spectrum of opinion in the loyalist community when we congratulate those who have shown great leadership within the socialist community and who have had the vision and taken great risks to create a new environment for the future where violence is no longer a viable option and where weapons are a thing of the past," it said.
Catholic primate Cardinal Sean Brady also welcomed the INLA's decommissioning.
Ireland Justice Minister Dermot Ahern said the move was another step towards guaranteeing peace.
"This is part of a series of decommissioning events carried out by paramilitary organisations in recent months," he said.
The paramilitaries announcements come just days after a historic deal was brokered that will see republicans and unionists share responsibility for running Northern Ireland's justice system.
The loyalist Ulster Volunteer Force decommissioned last year, while the loyalist UDA put its weapons beyond use last month. The IRA was witnessed destroying its cache almost five years ago.
The INLA was formed in 1974 and was known as a brutally violent organisation that also engaged in bitter internal feuds.
In 1979 it claimed the life of Conservative shadow secretary for Northern Ireland Airey Neave, a close associate of Margaret Thatcher, who was killed when a booby-trap bomb exploded beneath his car at the House of Commons.
Last October, the splinter group used a graveside oration outside Dublin to confirm its "armed struggle is over" and vowed to end its 35-year campaign of violence in Northern Ireland.