Only a few months ago, the 33-year-old Ireland lock did not expect to be part of what is now his third Lions mission. But with tour skipper Sam Warburton resting a knee injury, 2009 Lions captain O'Connell takes over as leader against the Barbarians.
"I suppose around Christmas, and even two or three months after Christmas, I certainly thought I wouldn't be here, so to be here and now captaining the side is fantastic," said O'Connell, who was laid low by groin and back problems.
"I am delighted. It's a very exciting occasion. We've had a few great weeks, and it has gone up another level since the Leicester boys and the Leinster boys came in. I am disappointed, obviously, for Sam. He has run a great ship the last few weeks."
Solitary Irishman O'Connell will take charge of a team containing nine Welshmen - including the entire back-row of Dan Lydiate, Justin Tipuric and Toby Faletau - three Scots and two English.
And head coach Warren Gatland has also selected a powerful bench containing the likes of Cian Healy, Alun-Wyn Jones, Jamie Heaslip and Jonathan Sexton, which could be important given current sweltering temperatures and punishing humidity in Hong Kong. Gatland has described Wales flanker Warburton's absence from the Baa-baas clash as "precautionary".
"Sam has just got a little knock," Gatland said. "He has had a little bit of a sore knee for the last 10 days, and the medics have just given him an injection and said just to stay off it for about five days. He was desperate to play, but we felt just so early in the tour it was not worth the risk.
"It is just precautionary, and there are two or three players in the same boat. Sean O'Brien has bruising on the bone, Rob Kearney's hamstring is just a little bit tight and Gethin Jenkins' calf is a little bit tight as well. They are all hopeful and confident of being fit for either the (Western) Force game next Wednesday or the game in Brisbane."
British and Irish Lions squad: S Hogg (Scotland); A Cuthbert (Wales), J Davies (Wales), J Roberts (Wales), S Maitland (Scotland); O Farrell (England), M Phillips (Wales); M Vunipola (England), R Hibbard (Wales), A Jones (Wales), R Gray (Scotland), P O'Connell (Ireland, capt), D Lydiate (Wales), J Tipuric (Wales), T Faletau (Wales).
Replacements: T Youngs (England), C Healy (Ireland), M Stevens (England), A-W Jones (Wales), J Heaslip (Ireland), C Murray (Ireland), J Sexton (Ireland), G North (Wales).