The National Treasury Management Agency has raised €4 billion at its first 30-year bond sale.
The auction drew strong demand despite record low interest rates and the NTMA moved more than halfway towards its 2015 issuance target after just five weeks.
Buoyed by a €1 trillion European Central Bank stimulus programme that will include government bond purchases, the NTMA sold the debt at a yield of 2.08%.
More than 350 investors had bid €11.2 billion for the 30 year bond, according to the agency.
The majority - 95% - of the interest came from overseas, it said, with 26% coming from British investors and 24% from Germany.
The NTMA said asset managers represented 45% of all investors, while fund managers represented a further 15%.
The syndicated deal follows seven and 15-year bond sales, also via syndication, since November that have allowed the agency to lock in cheap funding for years to come.
"They've really done a very good job of lengthening out the maturity of Ireland's debt, which will be looked favourably on by ratings agencies. There's a huge amount of positives attached to this deal," said Ryan McGrath, a bond dealer at Cantor Fitzgerald.
"Obviously there was huge demand, a lot of pension funds, a lot of life insurers, both from the UK and continental Europe," he added.
Demand was far in excess of the €2 billion deal size that market participants said would be typical of a benchmark 30-year issue.
The yield was also better the 3.2% Italy paid when it sold 30-year debt last month, shortly before the ECB announced its quantitative easing programme, which will buy bonds with maturities of up to 30 years.
When Ireland returned to short-term debt markets in July 2012 following a near two-year hiatus during the first part of its international bailout, it paid 1.8% to sell €500m of three-month paper.
But in common with most other euro zone bond yields, Irish borrowing costs have fallen sharply in the past year, aided by a growth rebound that saw Ireland's economy probably grow faster than any other European Union country in 2014.
The Central Bank today raised its forecast for 2015 economic growth to 3.7% from 3.4%, citing stronger consumer and investment spending.
The NTMA sold €4 billion in January's syndicated seven-year sale, out of planned issuance of between €12-15 billion of long-term bonds this year.
The NTMA fully pre-funded for 2015 last year. It plans this year to cover funding requirements for 2016 and to refinance bailout loans from the International Monetary Fund.
Barclays, Credit Agricole, Danske Bank, Davy and Royal Bank of Scotland had been joint lead managers for the auction.