Independent MEP Marian Harkin will not contest the next European Parliament election.
In a statement, she says she has served the people of the Midlands, North and West constituency for three terms and believes she has made a contribution in the most positive way.
"I came into politics from the voluntary sector, first as a TD representing Sligo/Leitrim and subsequently as an MEP," she said.
"During that time I have worked to represent ordinary people, community groups, workers, farmers, credit unions, carers, people with disabilities and many others.
"One of my objectives has always been to act as a bridge between Irish citizens and the European institutions particularly in regard to access and, of course, representation.
Bringing Europe closer to the citizen has never been just a slogan for me, it has been an essential part of my work.
"Politics is important, without good politics, society faces uncertainty, insecurity and confusion and all that flows from that."
The MEP also says she still has a huge interest in politics and aims, in some way, in the future to make a further contribution.
