Independent MEP Marian Harkin has said she will not contest the next European Parliament election in May.
The Midlands-North-West MEP has been in the European Parliament for nearly 15 years.
She was first elected in 2004 and was returned in 2009 and 2014.
In a statement, Ms Harkin said she still has a real passion for politics and that the EU is a vital force for good and a place where Ireland "can stand on its own two feet."
She said she had served the people of the Midlands-North-West constituency for three terms and made her contribution in the best way she could.
She said: "I came into politics from the voluntary sector, first as a TD representing Sligo/Leitrim and subsequently as an MEP.
"During that time I have worked to represent ordinary people, community groups, workers, farmers, credit unions, carers, people with disabilities and many others."
The MEP also says she still has a huge interest in politics and aims to make a further contribution in the future.
The announcement opens up the door for a new MEP in the Midlands-North-West constituency.
It is a four-seat constituency comprising the counties of Cavan, Donegal, Galway, Kildare, Leitrim, Longford, Louth, Mayo, Meath, Monaghan, Roscommon, Sligo and Westmeath and the city of Galway.
Dominic Hannigan Labour Party, Brendan Smith TD Fianna Fáil, Anne Rabbitte TD Fianna Fáil, Maria Walsh, Fine Gael, Mairead McGuinness MEP, Fine Gael, Matt Carthy MEP, Sinn Féin, Luke Ming Flanagan MEP, Independent, Saoirse McHugh, Green Party, Cyril Brennan, People Before Profit and Michael O'Dowd Renua have all confirmed that they will be putting their names forward.