Born in Castlebar, County Mayo, O'Neill first played competitive Gaelic football with the Castlebar Mitchels club. He was just eighteen-years-old when he won the first of four successive county senior championship medals in 1951. O'Neill first appeared on the inter-county scene as a member of the Mayo junior team. He won a Connacht medal in that grade in 1953, before making his senior debut during the 1953-54 league. O'Neill won a Connacht and National League medals with the team, however a dispute with the County Board over expenses saw him walk away from the side in 1956.[2]
His last appearance for Louth came in a 1962 Leinster Championship defeat to Dublin. He subsequently returned to Mayo and played his final game for the county side in 1963. That same year he won a fifth county SFC medal after rejoining Castlebar Mitchels. By then he had resigned from the Garda Siochana to join Calor Gas as Area Manager.[3] He would later work in management positions with Ireland West Tourism.[4] O'Neill ended his club career with Fr. Griffins in Galway.
In 2008, his autobiography 'Divided Loyalties' was released.[5]