Arlene Foster will take the reins in her first day as the sole unionist in the North's faltering powersharing government.
She was named acting first minister after the mass resignation of her party colleagues amid a crisis sparked by a murder linked to members of the IRA.
Democratic Unionist leader Peter Robinson has asked the DUP finance minister to remain in the Executive to prevent Sinn Féin from taking over key ministerial posts.
The unionist walkout from the mandatory coalition came after the DUP failed to get the Assembly adjourned for a period to allow crisis talks to address the implications of the murder of Kevin McGuigan to take place.
The political furore over the killing intensified on Wednesday when three senior republicans were arrested in connection with the murder.
As he announced the resignations, Mr Robinson repeated a demand for the British Government to suspend the institutions outright to enable space for the talks to happen. Northern Ireland Secretary Theresa Villiers last night rejected the call.
The fallout from the murder of Kevin McGuigan has already seen the Ulster Unionists resign their one ministerial post.
The exit of Mr Robinson along with three of the DUP’s four other ministers, and its one junior minister, has left the 13 minister administration in freefall. The departments of health and social care; social development; enterprise trade and investment; and regional development are now effectively rudderless.
Collapse of power-sharing is not inevitable but its demise appears to have been hastened by a day of dramatic developments at Stormont on Thursday.
The DUP wanted all Assembly business suspended to allow crisis talks to take place about the political consequences of the murder of Mr McGuigan.
Mr Robinson’s announcement came after Sinn Féin, the SDLP and the Ulster Unionists voted against a DUP proposal to adjourn the Assembly.
He issued a resignation ultimatum on Wednesday after the arrest of republicans Bobby Storey, Eddie Copeland and Brian Gillen over the fatal shooting of former IRA man Mr McGuigan. Mr Copeland and Mr Gillen remain in custody.
Police have said current members of the IRA were involved in last month’s shooting of Mr McGuigan in a suspected revenge attack for the murder of former IRA commander Gerard “Jock” Davison in Belfast three months earlier.
The disclosures about the IRA have heaped pressure on Sinn Féin to explain why the supposedly defunct paramilitary organisation is still in existence.
Ms Foster said she has stayed on the Executive in order to deter actions by what she called ``rogue'' republican and nationalist ministers.
She told BBC’s The View: “I have been placed there as a gatekeeper to make sure that Sinn Féin and the SDLP ministers don’t take actions that will damage Northern Ireland and principally, let’s be honest, that damage the unionist community.
“If anybody knows me and indeed knows the Democratic Unionist Party they know that I’m not going to put at risk to the people of Northern Ireland the possibility that rogue Sinn Féin or renegade SDLP ministers are going to take decisions that will harm the community in Northern Ireland.”
But her remarks drew criticism from Sinn Féin's Gerry Kelly, who described them as “bigoted” and a “throwback” to the past.
He told the broadcaster: “To make this attack on nationalism – because it wasn’t just republicanism, but on nationalism – and call ministers ’rogue ministers’ is a complete nonsense.”