Williams made his Wales senior debut against the Barbarians in 1996 and has gone on to be one of Wales' greatest ever servants.
Following Wales's early exit from the 2007 Rugby World Cup, Williams announced his retirement from the international stage. However, following the appointment of new Head Coach Warren Gatland, Williams was persuaded out of retirement and featured in every match of the Grand Slam winning tournament. He scored a try in the championship decider against France and was awarded the Man of the Match award for his superb performance against the Scots at the Millennium Stadium.
Williams was also one of the heroes of Wales's 2005 Grand Slam effort and was named the RBS Six Nations Man of the Championship, after a series of superb displays capped by the five-minute brace he scored against France.
Speaking of the 100 cap landmark, Cardiff Blues Chairman Peter Thomas said,
"I am absolutely delighted for Martyn and his family."
"He is without a doubt a legend in his own lifetime, for both Cardiff Blues and Wales.
"Martyn has been with us for well over a decade now.
"In that time has been a British Lion playing on three tours and to be finishing as a centurion is completely deserved, Martyn gives nothing but 100% in every game that he plays.
"You won't find a finer character on or off the field than Martyn.
"So for him and his family we are just absolutely thrilled and we shall be there to support him at the Baa-Baas game, when he runs out for his 100th cap."