New boss Steve Staunton handed the striker the captain's armband for his first game in charge - the friendly against Sweden at Lansdowne Road on Wednesday night.
Keano - vice-captain here at Spurs - is the Republic's record goalscorer with 25 goals from his 64 caps.
"You always dream one day you will captain your country but if I'm being honest, I didn't think it would come at the age of 25," said Robbie. "I thought I would have been older.
"At Spurs I've been given the role of vice-captain and when Ledley King has been out I've then been captain. It's something I've really enjoyed.
"I'm very honoured and privileged, and I'm grateful to Stan (Staunton) for putting his trust in me and believing I can lead this team.
"I certainly believe I can do it and I'm looking forward to what is a new chapter in my career and in Irish football also."
When asked as to what kind of leader he will be, Keane replied: "I'm not going to all of a sudden change overnight.
"I'd like to think I've got the respect of the players and if I can lead by example on and off the pitch that's the most important thing.
"I know I will always continue to give 100 per cent because I am so passionate about my country. Even if I wasn't captain I would continue to do that.
"But even though I am captain, every player on the pitch should be shouting. We should have 11 captains out there."
Robbie Keane said it was a dream come true to be named captain of the Republic of Ireland at the age of 25.