It features a memorial to 40 children killed by gunfire
The capital is gearing up for a weekend of celebrations to mark the 1916 centenary - one of which will be a new exhibition at the GPO.
An Post's new Witness History Visitor Centre was opened by acting Taoiseach Enda Kenny and acting Arts Minister Heather Humphreys.
The attraction is one of the permanent 2016 projects, for which the Department of Arts, Heritage and the Gaeltacht provided funds of €7m.
This allowed for construction and fit-out in the GPO's eastern inner courtyard.
An Post provided a further €3m for works such as cleaning and repairing facades, advance planning and marketing.
The interactive visitor attraction will bring history to life though technology, video, sound and artefacts.
It also includes special effects, soundscapes and stories of real people.
The centre-piece of the exhibition is an experience which puts visitors at the heart of the events of Easter week, when the GPO was both the rebels' military command centre and the seat of the provisional Irish government.
An Post has appointed Shannon Heritage to operate and manage the new centre.
The courtyard area also features a specially-commissioned memorial to the 40 children killed by gunfire during Easter week 1916.
Entitled 'They are Of Us All', it was created by internationally renowned Dublin artist Barbara Knezevic, using polished steel and 40 pieces of black limestone which came from the ruins of Jacobs biscuit factory.
Each stone represents a child.