Duncan Williams (born 17 April 1986) is an Irish rugby union player. He plays as a scrum-half and represents Cork Constitution in the All-Ireland League.

Williams made his Munster debut against Connacht in December 2009.^[1] He made his Heineken Cup debut against London Irish in October 2010.^[2] Williams also started against Australia in Munster's historic 15–6 victory over them in November 2010.^[3] He scored his first try for Munster in their 35–12 win against Scarlets in September 2011.^[4] He signed a two-year contract extension with Munster in March 2012.^[5]

He started for Munster A in their 31–12 2011–12 British and Irish Cup Final win against Cross Keys on 27 April 2012.^[6] On 28 February 2014, it was announced that Williams had signed a new one-year contract with Munster, which would see him remain in the province until at least June 2015.^[7] He signed a two-year contract extension in February 2015.^[8] On 2 January 2016, Williams earned his 100th cap for Munster when he came off the bench against Ulster.^[9] On 24 January 2017, it was announced that Williams had signed a contract extension which would see him remain with Munster until June 2019.^[10]

On 1 April 2017, Williams was a late replacement for the injured Conor Murray in Munster's line-up for the 2016–17 European Rugby Champions Cup quarter-final against Toulouse. Munster went on to win the game 41–16 and progress to the semi-finals.^[11] Williams earned his 150th cap for Munster on 10 February 2018, doing so when he started in the provinces' 33–5 win against Zebre in the 2017–18 Pro14.^[12] Facial injuries suffered during training initially ruled Williams out for the remainder of the 2017–18 season, as surgery was required,^[13] but he made a faster-than-expected recovery and returned to full training late in April.^[14] Williams was released by Munster at the end of the 2018–19 season.^[15]

After his release by Munster, Williams continued playing rugby at an amateur level for Cork Constitution. He had decided to retire from playing rugby after Con's All-Ireland League Division 1A final against Clontarf in May 2019,^[16] but after Con won the final 28–13 to secure their second AIL title in three years,^[17] Williams extended his playing career into the 2019–20 season, and he started in the 24–17 win against Young Munster in the final of the Munster Senior Cup in December 2019, a victory that secured a 30th title for the Cork side.^[18]

• Munster Profile
• Duncan Williams at European Professional Club Rugby
• Pro14 Profile