O'Neil was part of the squad at the 1968 World Cup and in 1969 was made the Kiwis captain. He won the New Zealand Rugby League player of the year award in 1969, being presented with the first Steve Watene Memorial Trophy. That year he was also the first winner of the Wellington Sportsman of the Year Award.
In 1970 O'Neil became the first player to play over 50 games for Wellington, he is currently the second most capped player, after finishing his career with 74 caps. O'Neil also played for the North Island in 1964 and 1965 and for Southern Zone from 1967 to 1969.
O'Neil again captained the New Zealand side in 1970 and made that year's World Cup squad. O'Neil toured Great Britain and France in 1971 before retiring at the end of that season.
He had played his entire club career with Marist, winning premierships in 1963 (shared), 1965 and 1971. In 1971 O'Neil served as a player/captain/coach of the club.