The striker is the first skipper of Steve Staunton's reign as Republic manager and takes over from the retired Kenny Cunningham. Newcastle goalkeeper Shay Given is vice-captain.
Robbie - our vice-captain here at Spurs - will lead his national team out for the first time in Wednesday's friendly against Sweden in Dublin.
Staunton said: "Robbie is a world-class player. Spurs have given him a lot of responsibility and he's handled it very, very well.
"Our lads respect him - the utmost respect - and I've given him a little challenge with this as well.
"He's certainly up for it and I'm sure he'll do a good job. He'll be very proud to do that job as well."
Keano is the Republic's record goalscorer with 24 goals and has already won 65 caps at the age of 25.
Staunton added: "If you have the respect of the players that's a big plus to start with and the fans see him as an icon.
"You only have to listen to the chorus on Wednesday night, the fans take to him, he responds as Shay does at other end.
"Those factors and the added responsibility will bring him on as a person and can make him an even better player."
Robbie Keane has been appointed the new captain of the Republic of Ireland.