O'Brien has signed a two-year deal with the club after leaving Barnsley at the end of last season and Coventry manager Steven Pressley played a big role in attracting him to the West Midlands.
O'Brien told the club's official website: "I'm delighted to get the deal done. The manager phoned me at the end of last season and told me he wanted to bring me in.
"It was one of the main reasons I signed for the club as it is always nice to be wanted.
"It's nice to be one of the first through the door as well because it is easier to settle into the squad.
"I had a few other offers but when I came down and met the manager, I knew this was the best option.
"The set-up here is extremely good and it was an easy decision.
"It has been good to get involved with the squad. It is a tight squad but some of the youngsters are really impressive."