"I see this as a continuation of what I have always done," he was reported as saying on Wednesday ahead of the Irish Open at the Fota Golf Club in Cork.
"I have been thinking about it a lot. I don't know if it is because the World Cup is in Brazil and I was thinking a couple of years down the line.
"I was thinking about all the times I have played for Ireland as a boy and everything. For me it is the right decision to play for Ireland."
McIlroy, who recently split from his fiancee, Danish tennis player Caroline Wozniacki, had earlier said "he would probably play for Great Britain", and in 2013 suggested he may miss the tournament altogether to avoid controversy over any decision.
"I was always very proud to put on the Irish uniform and play as an amateur and as a boy, and I would be very proud to do it again," he added.
"Just because now that I'm playing golf for money and I'm a professional, I'm supposed to have this choice or this decision to make, where if you look at the rugby players, you look at cricketers or hockey players, they view Ireland as one, the same as we do in golf.
"I don't think there's any point to change that or go against that just because it's a different event or it's the Olympics.
"I've had a lot of time on my own the last few weeks and just been thinking about it a lot. It's something that's been quite important to me and something that I needed to make some sort of decision or some sort of stand on it.
"Just weighing up everything, and thinking back about the times that I played for Ireland and won the European Team championship with Ireland, won a lot of great amateur titles representing Ireland, I just thought why change that?"
(Reporting by Josh Reich; Editing by John O'Brien)
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