The 23-year-old had his contract terminated by the Australian Rugby Union earlier this month following a string of off-field misdemeanors and was also released by Super Rugby side Melbourne Rebels.
But O’Connor, who has won 44 caps for the Wallabies, has joined Irish until the end of the season and is eyeing a fresh start.
“Having decided that I needed a change from both a personal and playing point of view I concluded the best way forward was to move to England,” said O’Connor, who could make his debut this weekend.
“London Irish offered me an environment that I felt comfortable with and play a style of rugby that appeals to me. I thoroughly believe I can improve elements of my game by playing in the Premiership.”
■ August 2011: One match ban and suspended fine for missing Australia’s Rugby World Cup announcement
■ June 2013: Photographed at a Burger King at 4am, three days before Test against British and Irish Lions
■ August 2013: Barred from flight to Bali and removed from Perth Airport by police for being intoxicated