O'Connell, 20, lived in Western Australia for several years as a child before returning to Ireland aged 11. He joins the Saints after being scouted by the club in June and July as he starred in the Gaelic Athletic Association (GAA).
"He was just named Cork Young Footballer of the Year. He was a young boy that actually lived in Australia for about seven years. He lived in WA. His mother's an Australian girl, his father is an Irishman so they lived in WA for seven years," St Kilda list manager Stephen Silvagni said.
"He did play Aussie Rules, Auskick and some early junior football. He actually has already adapted to the footy."