The 44 times capped Wallaby will make his debut this weekend against the Northampton Saints and will be part of the side until the end of the season.
O’Connor made his debut for the Wallabies at 18 in 2008 and since then has racked up 59 caps in Super Rugby for the Western Force and the Melbourne Rebels.
However after two troublesome years filled with alchol fuelled incidents no team in Australia will touch O’Connor with a barge pole, forcing the 23 year old to look for work elsewhere.
Commenting on his decision to join London Irish, O’Connor said: “Having decided that I needed a change from both a personal and playing point of view, I spoke to clubs in Japan and France, and concluded that the best way forward for my development was to move to England.”
London Irish Director of Rugby Brian Smith said: “James is a world-class player and a terrific kid and it is fantastic to have him at London Irish, He will bring a huge amount of experience to our group and will fit in well to our style of play. He is fit and ready to play so the coaching group will get him up to date on everything and hopefully he’ll be ready to go this weekend.”