It was while representing Swansea that Rees was first selected to represent Wales, brought into the team to face England in the opening game of the 1900 Home Nations Championship. Rees was not first choice for the match as in December 1899 the "South Wales Daily News" released the team sheet for the England vs. Wales encounter to be played on 6 January, with Gwyn Nicholls as centre. This was presumptuous as Nicholls had been part of the British Isles team that had recently toured Australia, and no contact had been made with Nicholls since the final game. On 31 December, a telegram was received stating that Nicholls would not be able to make the first Championship game, and the Welsh Rugby Union immediately responded with news that Rees would take his place at centre, winning his first cap alongside Swansea teammate George Davies. Wales won the game 13–3, with a try from Billy Trew on the wing, and a forwards try from Dick Hellings, both converted by captain Billy Bancroft who also scored a penalty goal. The "Athletic News" gave the Welsh victory to the pack, dismissing the threequarters, but "The Sportsman" wrote "an exposition of the three quarter back game was given which must have satisfied the great Mr Arthur Gould himself". The Thursday after the match, Nicholls arrived back in Britain and was immediately selected for the Welsh team to face Scotland. Despite a victory and some good reviews, Rees lost his place to Nicholls, despite Nicholls having not played a competitive game since the previous August. Some commentators believe that Nicholls played due to worries over his future selection caused by the good press articles the Swansea centres received. Wales won the next two games of the Championship without Rees, though his inclusion in the first game made him a member of the 1900 Triple Crown winning Welsh team.