Sinn Fein has declined to re-nominate a Stormont deputy first minister in a move set to collapse the powersharing executive in Belfast and trigger a snap election.
Barring a highly unlikely u-turn by the republican party, the institutions will now fall at 5pm today and Northern Ireland Secretary James Brokenshire will be legally obliged to call the election.
Sinn Fein declined to replace Mr McGuinness at the start of Assembly business at Parliament Buildings this morning.
The Sinn Fein veteran quit over the DUP’s handling of a botched green energy scheme.
Speaking in the Assembly today, Sinn Féin MLA Michelle O’Neill said there could be “no return to the status quo”.
She added: “The DUP have treated these institutions and sections of the community with contempt and arrogance.”
“Today Sinn Fein will not re-nominate for the position of deputy first minister.”
Ms O’Neill said Sinn Fein would only return to government if there was “real and meaningful change”.
Mr McGuinness’s resignation automatically removed DUP leader Arlene Foster from her position as first minister - as executive structures dictate one cannot govern without the other.
On Monday the DUP renominated Mrs Foster to the post. That was rendered meaningless by Sinn Fein’s subsequent refusal to renominate its own incumbent at the head of the executive.
Speaker Robin Newton said both ministers needed to be in post for their office to function.
“These requirements have not been satisfied today and the offices of the first minister and deputy first minister must remain vacant,” he said.
Ahead of the key Assembly session at Parliament Buildings in Belfast, Mrs Foster said the electorate did not want or need an election.
She accused Sinn Fein of triggering a poll because they did not like the outcome of last May’s vote.
“They have forced an election that risks Northern Ireland’s future and stability and which suits nobody but themselves,” she said.
Theresa May phoned Mrs Foster and Mr McGuinness early on Monday in a last-ditch effort to prevent the collapse of the devolved administration.
The Prime Minister’s official spokeswoman said Mrs May wanted to make sure Northern Ireland has “a voice” in the run-up to the start of EU withdrawal talks - expected to be triggered by the end of March with the invocation of Article 50 of the European Union treaties.
The Stormont Assembly will limp on until it is formally dissolved. An election is likely in late February or early March.
The failed reappointment process came at the opening of a full day of Assembly business during which a number of elements of the political crisis will be debated.
Emergency proposals aimed at reducing the RHI overspend are being proposed by DUP economy minister Simon Hamilton while Sinn Fein will also table a motion of no confidence in DUP speaker Mr Newton.
He has been under intense political pressure over his handling of a recalled Assembly session to debate RHI before Christmas.
The Speaker has also been forced to defend himself against conflict of interest accusations in regard to his handling of Assembly exchanges on a controversial charity in his east Belfast constituency.
The devolution meltdown has cast a shadow of uncertainty over a series of big ticket Stormont executive plans.
One of those is a payment scheme for households losing out under the UK Government’s so-called “bedroom tax” when it is introduced in Northern Ireland next month.
After Sinn Fein announced it would not replace Mr McGuinness, DUP Communities minister Paul Givan secured the necessary Assembly approval to roll out the bedroom tax scheme.
Ulster Unionist leader Mike Nesbitt was gearing up for the election.
“It is referendum time. You can have more of the same or you can have change. We are for change.”