Tickets for the concerts went on general sale at 10am on Thursday morning, with the Saturday gig almost sold out already and Sunday tickets selling fast.
A pre-sale event for fans who pre-registered got underway on Tuesday, while a separate pre-sale for MCD members kicked off on Wednesday.
The Dublin rockers headlined Sunday at Electric Picnic last weekend and closed out the show by announcing they were set to headline Slane.
Shortly after the announcement they would play Slane on Saturday, June 26, 2027, confirmation of a second date followed, with the second night scheduled for the following day on Sunday, June 27.
The second date was confirmed following significant demand for the initial date during the first pre-sale.
Slane boasts a concert capacity of 80,000 peoples, making these shows the biggest ever for the band.
Supporting acts will include Paramore frontwoman Hayley Williams, singer-songwriter Damien Dempsey and folk band Madra Salach, with more to be announced.
Tickets were priced from €89.25, including a €1 donation to homelessness charity Focus Ireland, and subject to a service charge of 12.5pc, up to a maximum of €10.50 per ticket.
Following in the footsteps of Thin Lizzy and U2, Fontaines DC will become just the third Irish act to headline Slane.
The two nights Slane form part of an EU and UK tour that will take the band to 20 cities across Europe, including Lisbon, Madrid, Berlin, Stockholm, Amsterdam and London.
Fontaines DC, comprised of lead singer Grian Chatten, guitarists Conor Curley and Carlos O’Connell, bassist Conor ‘Deego’ Deegan III and drummer Tom Coll.
This year’s concert at the Co Meath venue took place in July when US country singer Luke Combs played to a total crowd of around 160,000 across two nights.