Wales won the first official Six Nations Grand Slam in 2005.
Wales defeated all five of its opponents—England, Scotland, Italy, France and Ireland—to complete the Grand Slam. The achievement was Wales’s first Grand Slam since 1978 and its first outright Five or Six Nations championship since 1994.
The 2005 title was secured on the final day when Wales beat Ireland 32–20 at Millennium Stadium in Cardiff. Wales had already won away against France, England and Scotland, making the closing victory particularly significant.
The term Grand Slam means winning every match in a Five or Six Nations campaign. Wales had previously completed Grand Slams in the Five Nations era, but 2005 was the first such achievement after Italy joined and the competition became the Six Nations.