Mantle began his rugby career at a young age, playing for the Wales School team. As an adult he played with Bargoed before switching to first class team Newport. While representing Newport, Mantle was selected for his two Welsh rugby union caps. His first was when he was selected as part of the touring Wales team to Africa. Mantle played in the early games of the tour, including wins over East Africa in Nairobi, and Boland at Wellington. His first international was against South Africa in Durban in 1964, but Wales were outclassed and lost 24-3 in a one-sided match. Mantle played in the later games on the tour, including matches against Northern Transvaal and Orange Free State. On his return he played one final game in a win over England, at the Cardiff Arms Park as part of the 1963 Five Nations Championship. Mantle may have won more caps for Wales, but 'Went North', switching to the professional rugby league code when he joined St. Helens in 1964. He would later play for the Great Britain rugby league team. John Mantle played left-, i.e. number 8, in St. Helens' 2-25 defeat by the 1975 NSWRFL season premiers, Eastern Suburbs Roosters in the unofficial 1976 World Club Challenge at Sydney Cricket Ground on Tuesday 29 June 1976. He was coach of the Cardiff City Blue Dragons.
International games played
Wales rugby union
1964
1964
In rugby league Mantle was capped 13 times by Great Britain between 1966 and 1973, and won eight caps for Wales in 1975. He scored one try for Wales, giving him an overall total of 21 international rugby league appearances and three points.
John Mantle played in St. Helens' 35-12 victory over Halifax in the Championship Final during the 1965–66 season at Station Road, Swinton on Saturday 28 May 1966, in front of a crowd of 30,165.
John Mantle played and scored a try in St. Helens' 21-2 victory over Wigan in the 1966 Challenge Cup Final during the 1965–66 season at Wembley Stadium, London on Saturday 21 May 1966, in front of a crowd of 98,536, and played left-, i.e. number 11, in the 16-13 victory over Leeds in the 1972 Challenge Cup Final during the 1971–72 season at Wembley Stadium, London on Saturday 13 May 1972, in front of a crowd of 89,495.
John Mantle played right-, i.e. number 12, in St. Helens' 2-2 draw with Warrington in the 1967Lancashire County Cup Final during the 1967–68 season at Station Road, Swinton on Saturday 7 October 1967, and played left-, i.e. number 11, in the 4-7 defeat by Leigh in the 1970Lancashire County Cup Final during the 1970–71 season at Station Road, Swinton on Saturday 28 November 1970.