Williams qualifies for the Wales national team through his maternal grandfather Bill Rowlands from Gelli, Rhondda.
He made his international debut on 26 March 2008, two days before securing his move to Swansea City.
In the match, he played the full 90 minutes for John Toshack's men in their 2–0 friendly away win in Luxembourg, making an early error through a poor backpass to goalkeeper Lewis Price, but recovered possession in time.

On 1 April 2009, Williams scored an own goal in a 2–0 loss to Germany in qualification for the 2010 FIFA World Cup, deflecting Mario Gómez's cross at the Millennium Stadium.
He captained the country for the first time on 14 November in a 3–0 friendly win over Scotland at the Cardiff City Stadium.
On 11 October 2010, he scored his first international goal in a 5–1 friendly win over Luxembourg in Parc y Scarlets, finishing a header from debutant Steve Morison.

In October 2012, Williams was named captain of Wales by manager Chris Coleman, replacing Aaron Ramsey.
Coleman, who by that point had not won in his four matches, awarded the armband to Williams on account of his experience over the younger Ramsey.
The decision was criticised by Raymond Verheijen, the assistant to Coleman's predecessor, Gary Speed.

On 31 May 2016, Williams was named in Coleman's 23-man squad for UEFA Euro 2016, Wales' first major tournament for more than half a century.
On 1 July in Lille, Williams headed the equalising goal, against Belgium in the quarter-finals as Wales eventually won 3–1 to progress to the semi-finals for the first time in their international football history.
In the semi-final, Wales lost 2–0 to Portugal.
Williams qualifies for the Wales national team through his maternal grandfather Bill Rowlands from Gelli, Rhondda. He made his international debut on 26 March 2008, two days before securing his move to Swansea City. In the match, he played the full 90 minutes for John Toshack's men in their 2–0 friendly away win in Luxembourg, making an early error through a poor backpass to goalkeeper Lewis Price, but recovered possession in time.
On 1 April 2009, Williams scored an own goal in a 2–0 loss to Germany in qualification for the 2010 FIFA World Cup, deflecting Mario Gómez's cross at the Millennium Stadium. He captained the country for the first time on 14 November in a 3–0 friendly win over Scotland at the Cardiff City Stadium. On 11 October 2010, he scored his first international goal in a 5–1 friendly win over Luxembourg in Parc y Scarlets, finishing a header from debutant Steve Morison.
In October 2012, Williams was named captain of Wales by manager Chris Coleman, replacing Aaron Ramsey. Coleman, who by that point had not won in his four matches, awarded the armband to Williams on account of his experience over the younger Ramsey. The decision was criticised by Raymond Verheijen, the assistant to Coleman's predecessor, Gary Speed.
On 31 May 2016, Williams was named in Coleman's 23-man squad for UEFA Euro 2016, Wales' first major tournament for more than half a century. On 1 July in Lille, Williams headed the equalising goal, against Belgium in the quarter-finals as Wales eventually won 3–1 to progress to the semi-finals for the first time in their international football history. In the semi-final, Wales lost 2–0 to Portugal.
Ashley Williams (footballer)