On the 10th April 1998 the Belfast/Good Friday Agreement was signed and referendums on the Agreement were held and passed in both parts of Ireland. Following elections the first power sharing Assembly met in July 1998 but failed to form an executive until December 1999.  It has operated intermittently and been suspended on five occasions; the longest from 2002 to 2007. The current 6th Assembly was suspended in 2017 and reconvened in January 2010.

The early years of the Assembly were preoccupied with decommissioning of paramilitary weapons, demilitarization of the British army, and reforms to policing. Most of the suspensions were due to Unionist pressure on decommissioning. The IRA required assurances and evidence of the demilitarization by the British Army and real reforms to policing. Once measures were taken by the British government the international decommissioning body was able to verify that arms belonging to paramilitaries were being decommissioned. In 2005 the IRA declared "an end to its armed campaign". By 2010 similar statements had been issued by almost all paramilitary groups.

The first Assembly was led by the Ulster Unionist Party (UUP) and the Social Democratic and Labour Party (SDLP).  In the 2003 elections the Democratic Unionist Party (DUP) and Sinn Fein, emerged as the two leading parties. The DUP were opposed to the Belfast Agreement. Therefore, the British Government did not restore power to the Assembly and the elected members never met. In October 2006, the governments and the parties, including the DUP, made the St Andrews Agreement and a new transitional assembly came into effect. The British government agreed to fresh elections for 2007.

In the 2007 elections Sinn Fein and the DUP expanded their representation. Famously Martin McGuiness and Ian Paisley worked together as the "chuckle brothers" in this Assembly. The position of the DUP and Sinn Fein was retained in all later elections. The last election in 2017 marked a significant shift in Northern Ireland's politics, being the first election since Ireland's partition in 1921 in which unionist parties did not win a majority of seats, and the first time that unionist and nationalist parties received equal representation in the Assembly.

Not everyone supported the Good Friday Agreement. In July 1998 an ongoing dissident IRA campaign began. One of the first actions was the Omagh bombing that killed 29 civilians. The recent move to "Brexit" had the potential to escalate the dissident campaign if a "hard land border" emerged.