Head coach Sir Clive Woodward named a strong side for the tourists' first game of six before the opening Test against New Zealand on June 25, and Williams cannot wait for the action to begin.
The Welsh flanker said: "It is great to be selected for the first game and I can't wait to get out there after all the build-up.
"We know there will be no easy games on this tour and Bay of Plenty will be determined to give us a stiff test but we are looking forward to the challenge."
Debutant O'Connell echoed the thoughts of his team-mate and admitted it was a pleasure to be named in the same side as him.
"It will be a tremendous honour for me to have the opportunity to pull on a Lions jersey for the first time," said the Ireland second row.
"Looking at the team sheet, it is really exciting to play alongside players of such quality, names like Lawrence Dallaglio and Martyn Williams, who I have admired for such a long time.
"It will be a great experience and an important test for both me and for the team."