The South African-born midfielder signed a three-year deal at Hillsborough and it is hoped that he will be an integral part of the Owls set-up.
He admits not being fully fit at the moment because he is still catching up on pre-season training following his late switch from Livingstone but he is adamant he will be ready for the new season.
He told Footymad: "I have come to the club a little later than the rest of the guys so I am probably lagging behind fitness wise but I am sure I will catch up and be ready as soon as possible."
On his ill-fated spell at Ewood Park four years ago, O'Brien is aiming to prove that he can hack life away from Scotland by impressing for his new club.
He said: "I had a period down south a few years ago at Blackburn and it didn’t go that well but the plan was always to come back down here when the right club and manager show an interest. I am at the age now where I can give it another chance and I am looking forward to it.
"I’m an attacking left-footed midfielder and I am sure that the fans will make their own mind up about me over the season but that’s my strengths, going forward, setting up goals and hopefully scoring a few along the way.
"I know that the championship will be a very tough league next year because there are a lot of big, big clubs in it but I think with the squad we have got we can definitely do well and stay in the league, anything else will be a bonus."