The fourth Northern Ireland Assembly was the unicameral devolved legislature of Northern Ireland following the 2011 assembly election on 5 May 2011. This iteration of the elected Assembly convened for the first time on 12 May 2011 in Parliament Buildings in Stormont, and ran for a full term.

The election saw 18 Assembly constituencies return six Members of the Legislative Assembly (MLAs) each. The Democratic Unionist Party (DUP), led by Peter Robinson, remained the largest unionist party and the largest overall. Sinn Féin, led by Gerry Adams, remained the largest Irish nationalist party and the second largest overall. As per the Belfast Agreement and the St Andrews Agreement, a power-sharing coalition was then formed with the DUP, Sinn Féin, the Ulster Unionist Party (UUP), the Social Democratic and Labour Party (SDLP) and the Alliance Party of Northern Ireland. William Hay was elected as Speaker in the first sitting of the Assembly. Following Hay's retirement, Mitchel McLaughlin was elected as the first nationalist Speaker in October 2014.