An Bord Pleanála has overruled Cavan County Council's decision to refuse planning for a mast.
Eir can now proceed with developing the 18 metre high structure in Killeshandra.
The board ruled that the multi-operator monopole and antennas at the Eir Exchange on Railway Road wouldn't impact on visual or residential amenities.
This contradicted the opinion of planners in Cavan County Council and An Bord Pleanála's planning inspector.
The order added that the chosen location was suitable for receiving 2G, 3G and 4G coverage in the area.
Six additional conditions were added to the permission.