South African-born Thomas was part of the youthful squad that toured Argentina in the summer of 2006, he subsequently gained his debut cap for Wales on the tour. Thomas has also represented Wales at U19 and U21 levels.

The start of the 2006–2007 season saw Thomas incur a heart scare which kept him out of action for six months; he made only six appearances at the start of the season and just four in April and May 2007.

Thomas received a call up to the Wales squad ahead of the two-Test tour of Australia in May but he sustained ankle ligament damage which ruled him out of action. In June he was named in Gareth Jenkins's 41-man preliminary Rugby World Cup 2007 summer training squad but unfortunately did not make the final cut.

In November 2007 Thomas was included in Caretaker Coach Nigel Davies's squad to face South Africa in the initial Prince William Cup match at the Millennium Stadium; he made the starting XV in the defeat to the world champions.

January 2008 saw Thomas receive a call-up to Warren Gatland's RBS Six Nations squad; the prop started in the superb victory over the Azzurri at the Millennium Stadium in the Grand Slam winning campaign.