The National Treasury Management Agency has bought back almost two-thirds of the €6.8 billion outstanding on a bond due to mature in January.
The move will improve the Government's debt position as the end of the year approaches.
The €4.1 billion buyback has no impact on the funding the agency has raised to meet its needs into the first quarter of 2015, but was purely a matter of timing, the NTMA said in a statement.
"The Exchequer remains fully funded for all of 2014 and into the first quarter of 2015," the agency added.
Finance Minister Michael Noonan said earlier that the buyback would likely mean Ireland's Government debt would peak at 122% of gross domestic product this year, rather than the 124% previously forecast.