Explainer-How is Northern Ireland governed and what's next after DUP deal?

BELFAST (Reuters) - Northern Ireland's largest pro-British party said on Tuesday it had agreed a deal with the United Kingdom government on the operation of post-Brexit trade rules that would pave the way for it to return to the region's power-sharing government.

Northern Ireland has had no government for almost two years, since the Democratic Unionist Party (DUP) walked out in protest over a trade deal with the European Union, which it said undermined Northern Ireland's place in the UK by requiring checks on some goods coming from Britain.

The party's leader said the power-sharing government - a key part of the 1998 Good Friday peace agreement - could be restored within days if the British government acted quickly.

HOW DOES NORTHERN IRELAND'S DEVOLVED GOVERNMENT WORK?

Irish nationalist and pro-British unionist politicians are obliged to share power in the British-run region under the terms of the accord that ended three decades of sectarian violence in Northern Ireland.

However, power-sharing has broken down on several occasions, and the provincial assembly and executive were also suspended between 2017 and 2020.

WHY WAS THE GOVERNMENT SUSPENDED THIS TIME?

When Britain left the EU, it agreed in effect to leave Northern Ireland within the bloc's single market for goods, given its open border with EU member Ireland, enshrined in the Good Friday agreement.

But this put it at odds with Northern Irish unionists, and the DUP quit the government in February 2022 when the checks underpinning the deal began to be implemented. It also opposed a reworked agreement, the Windsor Framework, struck a year later, to reduce the number of checks required on some goods coming from Britain by introducing 'green' and 'red' lanes.

DUP leader Jeffrey Donaldson said on Tuesday the offer from London to legally cement Northern Ireland's place and trading position in the UK was sufficient for the party to end its boycott.

WHAT HAPPENS NEXT?

Northern Ireland's main parties were due to meet to discuss, and most likely agree to, the restoration later on Tuesday, with Donaldson tying his party's return to the British government "fully and faithfully" delivering on what had been agreed, including passing the new legislation.

He said the government could publish a bill as soon as Wednesday. A member of Prime Minister's Rishi Sunak's government said it could be presented to parliament on Thursday.

Once it passes, the Northern Irish parliament at Stormont will meet to elect a first and deputy first minister. For the first time, Irish nationalists Sinn Fein will take the role of first minister after an historic election win shortly after the DUP walkout.

WHAT OBSTACLES ARE AHEAD?

All sides want to move quickly before critics, particularly hardline unionists opposed to any compromise, unpick the proposals and imperil the restoration of the regional government.

Donaldson refused to disclose the margin by which his party's executive voted to accept the new deal on Monday.

Jon Tonge, Professor of Politics at the University of Liverpool, told the BBC that DUP lawmakers could yet make trouble, but that he was confident the devolved government would be quickly restored.

Irish Prime Minister Leo Varadkar said the EU would also need to check that the deal did not infringe the Windsor Framework or Good Friday Agreement, but told reporters he did not anticipate any problems.

(Reporting by Padraic Halpin and Amanda Ferguson; editing by Elizabeth Piper and Kevin Liffey)