Dublin MEP Gay Mitchell will not contest the European Parliament elections next year.
The Fine Gael MEP - and former presidential candidate - made the announcement in Strasbourg today, saying now is a good time to allow new candidates to emerge.
By the time the 2014 election comes around, he will have served as an MEP for a decade - and 26 years as a TD.
Mr Mitchell said the constant travelling between Dublin, Brussels and Strasbourg influenced his decision.
"I'm very interested in things like economic and monetary affairs," he said.
"I'm interested in the Third World where a lot of children are dying - 23,000 every day.
"But the downside to this job is that you are constantly travelling between three places. I've three offices - one in Strasbourg, one in Brussels and one in Dublin.
"And then you are also travelling to places outside of the European Union, so that takes its toll."
Taoiseach Enda Kenny paid tribute to Mr Mitchell, calling him "a politician of deep conviction who has always approached his many roles in public life with great commitment and integrity".
"I thank him for his many years of dedicated service to his constituents in Dublin and to the country as a Councillor, as Lord Mayor of Dublin, as Dáil Deputy, as Minister of State and as an MEP for Dublin," Mr Kenny said.
"I wish Gay, his wife Norma and their family every health and happiness in the future."