An Bord Pleanála has given the go-ahead for a 47-kilometre motorway scheme between Clonee and Kells, subject to ten listed modifications.
The motorway has an estimated price tag of €600m and will have two tolls.
The Bord said it was granting approval because it was necessary to provide adequately for the existing and projected traffic growth, and the plan would be in accordance with proper planning and sustainable development.
Meath County Council told a public hearing that the motorway would run for 60 kilometres in total and predicted it would cut the traffic volumes through Dunshaughlin and Navan by as much as three-quarters.
However, the heritage body Dúchas, which has since been abolished by Environment Minister Martin Cullen, expressed archaeological concern because the road passed close to the historic Hill of Tara.
In its decision, An Bord Pleanála called for a survey to be conducted.
