The new Children's Hospital of Ireland should be open by the end of 2014, the hospital development board has said.
Subject to planning permission, building will begin next year and construction should finish by the end of 2013, after which it will be fitted out.
An ambulatory and urgent care centre will also open at Tallaght Hospital in 2013.
Minister for Health Mary Harney described the new hospital as the number one building project which would mean savings of around €25m a year when the three hospitals came together.
She promised that it would open in 2014. It will have up to 399 beds and 800 car parking spaces.
Single rooms will be available for each inpatient with space for parents to sleep over.
The consortium chosen to design the hospital is Murray O'Laoire - Brian O'Connell - NBBJ, which has designed over 30 children's facilities.
Three hospitals are due to transfer to the facility - Temple St, Our Lady's in Crumlin and the National Children's Hospital at Tallaght.
The location of the new facility, beside the Mater Hospital, was decided on by the HSE in June 2006, following a recommendation from an independent task force.
The decision was criticised by Our Lady's Children's Hospital, which said the site could not deliver a world class facility.
The Tallaght Hospital Action Group also raised concerns about limited parking and access to the hospital in the centre of Dublin.
At a briefing to outline more details of the design, Taoiseach Brian Cowen said building work will start by the last quarter of 2010.
Mr Cowen said that all three children's hospitals are fully engaged in progressing the plan.
He said that currently the cost of running the three hospitals was €250m a year and that the new facility would harness economies of scale.
