Eir has said a new €500m investment in so-called fibre-to-the-home broadband will provide coverage to every town in the country with more than 1,000 homes and businesses.
The firm said its fixed network investment programme would provide coverage to another 1.4 million premises with speeds of up to 10 Gbps.
Fibre-to-the-home is where fibre is connected directly to individual buildings such as houses, apartments or businesses, instead of the traditional broadband which uses so-called "cabinets", which are on the street.
Connecting directly to a home is what allows superfast broadband, with movies downloaded in seconds.
Eir said its new rollout would begin once its already underway €250m connection to 335,000 rural premises was completed in June.
The firm's chief executive Carolan Lennon said the plan would "deliver not just the fastest and most extensive fibre network in Ireland, but also one of the most extensive in the whole world".
Eir was one of the original bidders for the long-promised National Broadband Plan, which has been in limbo since first mooted in 2012, before pulling out.
The plan, which promised to connect 540,000 hard-to-reach homes and businesses around the country, has still no start date, despite just one bidder being left.
Finance Minister, Paschal Donohoe said last week the bid was still being examined by Department of Communications officials.
Meanwhile, Siro, the joint broadband venture between the ESB and Vodafone, said it was investing €14m to cover six towns in Donegal.