O'Connor, who has played on the wing and at full-back for the Wallabies, will line-up opposite his new Melbourne Rebels team-mate Danny Cipriani.
Australia are without injured fly-half Quade Cooper and coach Robbie Deans has opted to start with Berrick Barnes at inside centre.
O'Connor has experience at fly-half, having played there for the Western Force in last season's Super 15 campaign and he has been training in the role since Australia arrived in London.
The Wallabies will be captained by flanker David Pocock, with World Cup skipper James Horwill to start from the bench.
Australia team v Barbarians: A Ashley-Cooper; L Turner, R Horne, B Barnes, D Ioane; J O'Connor, W Genia; J Slipper, T Polota-Nau, S Ma'afu, R Simmons, N Sharpe, S Higginbotham, D Pocock (capt), B McCalman.
Replacements: S Moore, B Alexander, J Horwill, D Dennis, M Hodgson, N Phipps, B Tapuai.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
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Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
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The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.