Williams made his Munster debut against Connacht in December 2009. He made his Heineken Cup debut against London Irish in October 2010. Williams also started against Australia in Munster's historic 15-6 victory over them in November 2010. He scored his first try for Munster in their 35-12 win against Scarlets in September 2011. He signed a two-year contract extension with Munster in March 2012. He started for Munster A in their 31–12 2011–12 British and Irish Cup Final win against Cross Keys on 27 April 2012. On 28 February 2014, it was announced that Williams had signed a new one-year contract with Munster, which will see him remain at the province until at least June 2015. He signed a two-year contract extension in February 2015.