More than 10,000 fans of the American country music singer had queued outside ticket outlets - some since Sunday - in a desperate attempt to secure their place at Croke Park in Dublin.
It will be the first time the star has performed in Ireland since 1997.
Before the sale, Ticketmaster Ireland said it had doubled staff numbers at its call centres and had even put security at ticket outlets.
As tickets went on sale at 9am it tweeted that its website was already "VERY busy" and asked fans to be patient.
@Karenmccarthy2 tweeted: "I don't think I have ever experienced stress like I did this morning!! #GarthBrooks tickets in the bag!!!"
@alisoncolhoun wrote: "55 mins in @TicketmasterIre virtual queue and a heart stopping visa verify later... #GarthBrooksCrokePark tickets in the bag #relief"
The first two dates, Friday and Saturday July 25 and 26, had sold out by around 10am and a third date, for the Sunday, was added.
Ticketmaster said just before 11 a.m. that this date had also sold out, leading some fans to take to Twitter to plead for a fourth date to be added.
The company said all 240,000 tickets had been bought in 90 minutes.
Ticketmaster said it was the first time an artist has sold out three dates at Croke Park in one day.
Bob Doyle, Garth Brooks' manager, said: "We're thrilled."
Brooks, who is the best-selling albums artist in the US, retired from music in 2001 but in 2009 he began a five-year concert deal with a hotel in Las Vegas.
The Croke Park shows are not part of the world tour, but are one-off specials in advance of his world tour next autumn.
(c) Sky News 2014
Original headline: Garth Brooks Tickets Sell Out In 90 Minutes
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