[5] Before his first international match Roos faced the 1903 touring British Isles while representing Western Province; the game ending in a 3–3 draw at Newlands.

[6] After his performance for Western Province, Roos was selected to represent the South African national team in 1903 in the final Test against the British Isles.

[4] After being given the captaincy, Roos addressed the team by stating, "I would like to make absolutely clear at the outset we are not English-speaking or Afrikaans-speaking, but a band of happy South African"; as the tour took place just several years after the end of the Second Boer War, where once teammates had fought on different sides of the conflict.

Roos was forced to miss the game after he injured his collarbone in the encounter with Oxford University,[9] and the captaincy was handed over to Paddy Carolin; the match ended in the first defeat for the South African's with Scotland scoring two tries in the second half.

The Glamorgan team that had run the South Africans close earlier in the tour had contained twelve internationals, and the Welsh were keen for revenge.

South Africa beat Newport by a goal and a try to nil, and after the game the two team captains sat down at the Westgate Hotel for a post-match dinner.

Wales selected a strong team, with Teddy Morgan and Johnnie Williams on the wings, and captained by talismanic three-quarter Gwyn Nicholls, who had come out of retirement to lead the Welsh.

Roos started the match with heavy strapping to protect an injured shoulder,[15] and several of his team were suffering from coughs and sore throats brought on by the British winter weather.

[15] Although the Welsh started at a fast pace, the South Africans soon began to launch their own attacks and the firm surface of the St. Helen's pitch played to the Springbok's strengths.

At the final whistle the South African supporters, assisted by Welsh fans, rushed onto the pitch and carried Roos from the field.

[17] A week later the South Africans faced England at Crystal Palace and Roos was fit enough to lead his team out against international opposition for the third time.

As the tour headed towards its end, the South African's took control of the matches once again, beating Lancashire narrowly, but with decisive wins over Cumberland, Surrey and Cornwall.

At the after-match dinner at the Queen's Hotel in Cardiff, Roos stood to make a speech, "It is only human to be disappointed in having been beaten... but I am glad for one man's sake that you had such a glorious success, and that is our friend Gwyn Nicholls.

"[22] The final match of the series was against a France XV, and was played at the Parc des Princes in Paris on 3 January 1907, just two days after the Cardiff defeat.