She will leave her Democratic Unionist Party (DUP) role on May 28 and will quit as First Minister of Northern Ireland at the end of June.
So who will replace her in her role as leader of the DUP?
Why has Arlene Foster quit the DUP?
Mrs Foster, who has been leader of the party for more than five years, said the staggered timeline for her departure was designed to “give space” for the process of electing a successor.
“It has been the privilege of my life to serve the people of Northern Ireland as their First Minister and to represent my home constituency of Fermanagh/South Tyrone,” she said.
Her departure comes as multiple DUP sources told the Belfast News Letter that a clear majority of DUP Members of the Legislative Assembly - as well as at least half the party’s MPs and some of its peers - levelled a letter of no confidence in Mrs Foster.
Why did DUP members want her out?
Foster, the third leader in the party’s history, replaced the retiring Peter Robinson unchallenged in 2015, in the same way he had succeeded party founder Ian Paisley in 2008.
There has been growing unease among DUP members about Mrs Foster and the wider party leadership in recent months.
The primary source of concern is the handling of the Brexit process. The DUP is facing anger from the wider loyalist and unionist community for the introduction of an Irish Sea border.
Critics have accused Mrs Foster of failing to use the party’s influence at Westminster – particularly during its confidence and supply deal with the Conservatives – to secure a Brexit deal that would see Northern Ireland leave the EU on the same terms as the rest of the UK.
Who are the potential candidates to lead the DUP?
There are a number of contenders that could emerge as either DUP leader and/or First Minister following Mrs Foster’s departure.
Rules on double jobbing mean a sitting MP could not be First Minister and there have been suggestions the party faithful might prefer to split the two positions, with a leader based in Westminster while another senior member takes the reins at Stormont Castle.
The model is not without precedent and is already operated by the DUP’s partners-in-government, Sinn Fein.
The contest, when it is held, will involve a very small electorate – only the party’s MLAs and MPs will get a vote.
These are the most likely candidates to take over from Arlene Foster:
Sir Jeffrey Donaldson
The long-standing Lagan Valley MP is the party’s current leader at Westminster. The former Ulster Unionist is seen as a moderate whose political outlook would be broadly in line with Mrs Foster’s. There is a sense that the traditional wing of the DUP never quite trusted Mrs Foster due to her UUP roots and Sir Jeffrey would face a similar challenge if he was to succeed her.
– Edwin Poots
Stormont’s current Agriculture Minister. An experienced ministerial operator who has held a number of senior executive portfolios. Has made little secret of his political ambitions and is seen by many as the leading contender to replace Mrs Foster. Viewed as a hardliner, he would be more aligned with the religious fundamentalist/Paislite wing of the party. Has found himself in an awkward position of late as the minister with responsibility for implementing the checks required under the Northern Ireland Protocol – a factor that could work against him.
– Gavin Robinson
MP for East Belfast and former lord mayor of Belfast. The face of the party’s young generation. A former barrister, Mr Robinson is seen as a very capable operator. He would also be viewed as a political moderate.
– Sammy Wilson
Was tempted to challenge for the job in 2015 but ultimately did not run after Peter Robinson made it clear that Mrs Foster was the preferred candidate to succeed him. The arch Brexiteer is a popular figure with the grassroots and would be viewed as another hardliner. Whether he would consider running this time round is unclear. His opportunity to do so may have come and gone in 2015.
– Nigel Dodds
In normal circumstances, the deputy leader would be well placed to succeed the leader. However, the internal criticism of Mrs Foster has extended to Lord Dodds and it would be highly unlikely that he would be seen as the “change” candidate the rank and file are hankering for.
– Ian Paisley
The son of the party founder, Mr Paisley has a very significant personal following within the DUP. However, he is sometimes viewed as somewhat of a maverick who ploughs his own furrow in the Paisley stronghold of North Antrim. His standing within the party outside of his constituency heartland has been dinted by a series of controversies involving the non-declaration of foreign trips with the parliamentary authorities.
Additional reporting by PA.