Rugby was suspended for the duration of World War II and after the end of hostilities Tamplin joined Cardiff.
Tamplin was selected to represent his country late in his rugby career when he was chosen to play, in the 1947 Five Nations Championship.
Tamplin also scored in the next two games of the Championship, with the winning penalty goal against France, and a conversion in the Irish match.
When Tamplin was selected to face Australia, he was still a Cardiff player, and as well as leading the Welsh team he also scored all the points in a victory over the Australians after two successful penalty kicks.
In the 1948 Five Nations Championship, Tamplin played in three games, drawing against England, beating Scotland, but most importantly, losing on home soil to France.