O'Connell, a lock who was capped 108 times by Ireland and played seven tests for the British and Irish Lions, is known for his inspirational talks and Clarke wanted him to speak to his players ahead of Friday's opening foursomes matches.
"Part of my whole thought process for this week is 'shoulder to shoulder', one team, one unit," Clarke told reporters on the first day of official practice at a sunny and windy Hazeltine.
"As you know, shoulder to shoulder with the rugby background that I have as well, it resonated with me. It was something that I pursued through my captaincy.
"There's no finer an example of 'shoulder to shoulder' than Paul O'Connell. He has legendary status, both at home and in terms of leading the British Lions who always play away from home."
O'Connell, who captained both Ireland and the British and Irish Lions before retiring from professional rugby in February this year, is his country's third most-capped player of all time.
"With us being away from home, he was my choice to come and address the team this evening," said Clarke, who is bidding this week to lead Europe to a fourth successive Ryder Cup victory, and their ninth in 11 editions.
Asked whether he would use NBC commentator Johnny Miller's assertion that this was a decidedly weak European team as extra motivation for his players, Clarke replied: "I don't need to. The guys have all seen everything that's been said.
"But in terms of that, we have the Masters champion (Danny Willett), we have the (British) Open champion (Henrik Stenson), we have the Olympic champion (Justin Rose) and we have the FedEx champion (Rory McIlroy).
"You combine that with all the experience and with all of the rest of the team and the way those guys have played, I don't really need to respond to that. I think I've got full confidence in our team."
During broadcast of last week's Tour Championship eventually won by McIlroy, Miller said: "I do believe the Euros have got, at least on paper, the worst team they've had in many years."
(Editing by Andrew Both)
