Xavier grew up in Blackburn with his parents and three other siblings, two older sisters and his younger brother. He attended Whitefriars College and completed his VCE at the end of 2018.

Xavier was selected by the West Coast Eagles with Pick 28 in the 2018 National Draft. He has speed and agility and is prominent at stoppages and can push forward to use his goal sense to impact the scoreboard. Coming into a Premiership winning midfield, O’Neill had to work hard to earn his debut, which came in Round 13 of the 2020 season and was capped off with a goal.