The 36-year-old, who is the nation's leading goalscorer with 67 goals, announced last Thursday that he would retire from international football following Wednesday's friendly against Oman.
"It's been an emotional week. It's been surreal. I've dreaded this day for a long time [but] it's the right time for me," said the former Tottenham Hotspur and Liverpool forward in a press conference on Monday.
"To the fans, it's been an incredible journey and something I'll never forget. Wednesday night will be very emotional.
"The defining moment of my career was being given the Ireland captain's armband at the age of 26. It was a big moment for me.
"I've had so many wonderful memories, but it's the right time. I've played for 18 years. You can't please everybody. All I ever wanted was to do my best for my country. I think I did okay."