Fine Gael MEP Seán Kelly has ruled himself out of seeking his party's nomination for the presidency.
The election to replace Michael D Higgins is expected to take place later this year.
So far, only former Fianna Fáil minister Mary Hanafin has said she is interested in the role.
Sinn Féin said it has "not ruled out" a presidential run for its leader, Mary Lou McDonald, while former RTÉ broadcaster Joe Duffy said he is not considering a run for the Áras.
Speaking to RTÉ's Morning Ireland, Mr Kelly said he had given it a lot of consideration but will not be running, adding that it was the "most difficult decision" of his political life.
The Ireland South MEP said he asked himself if he was happy with what he is doing at the moment and whether he would be happier spending seven years at Áras an Uachtaráin.
"Perhaps not," he said.
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Mr Kelly said the presidency is a "once in a lifetime" opportunity and an "awful lot of TDs" and supporters both within Fine Gael and outside the party were anxious for him to run.
"I had to make up my own mind, having consulted with my family," he said, adding that his family was "100%" behind whatever decision he made.
He said he has responsibilities in Europe and the best thing would be to continue the work he has been doing there.
"My mind was never made up and I was thinking seriously about it," he said.
"When I look at it deeply, it's a largely ceremonial role and you don't have that much power and influence ... I like to be involved politically."
Former EU Commissioner Mairead McGuinness has been widely tipped as the likely Fine Gael candidate.
Mr Kelly described her as a very good prospect and said he would support her if she is the party's choice.
"I'm sure I, and all Fine Gael people, will support her," he said, adding that he would have welcomed a contest but that would require more than one candidate.
"There's still plenty of time, let's see how it pans out," he said.
"I wanted to make up my mind today so that people would have an opportunity to nominate whoever they wanted to in due course."
