Mark James Williams MBE (born 21 March 1975) is a Welsh professional snooker player who is a three-time World Champion, winning in 2000, 2003 and 2018.

[6] After failing to qualify for the 1996 World Championship, he won the first ranking event of the new season in October 1996, the Grand Prix, beating surprise finalist Euan Henderson 9–5.

[8] He also beat Hendry in a "thrilling" final in February 1998, to take his first Masters title, winning 10–9 in a black-ball finish in the deciding frame, after recovering from 6–9 down.

[28] Before the 2003 World Championship he had a scare with his cue when it was damaged and bent on his flight with Ryanair to play in the Irish Masters, but he had it repaired before the tournament.

[39] On 26 March 2006, Williams won his 16th ranking event, his first in two and a half years, at the 2006 China Open in Beijing, beating John Higgins 9–8 in the final.

He also showed good form in the 2006 World Championship, beating Anthony Hamilton 10–1 and Mark Selby 13–8[41] to set up a quarter-final clash with Ronnie O'Sullivan, the first time the two had met at the Crucible.

[46] However, Williams had perhaps the worst season of his career in 2006–07, losing his first match in several tournaments, including the 2007 World Championship, where he lost 9‍–‍10 to Joe Swail.

[49] After a 2–6 first round loss to Ken Doherty in the 2008 Masters, Williams revealed he was considering retirement from the game if he dropped out of the top 32 and was forced to play in all the qualifying competitions, although then only 32 years old.

At he UK Championship his form inproved as he beat Mark Selby[54] and Graeme Dott 9–7, before losing narrowly 8–9 to Ali Carter.

[64] On his way he beat Jamie Cope 5–3, the then reigning world champion John Higgins 5–2, Marco Fu 5–1, and Ali Carter 6–4, setting up a clash with Ding Junhui in the final.

[90] Williams caused a degree of controversy ahead of the World Championship by stating on his Twitter page that he "hates" the tournament's venue, the Crucible Theatre, and hopes it will be played in China soon.

[94] Williams first ranking event of the 2012–13 season was the 2012 Wuxi Classic, where he beat Tom Ford and Mark Allen, before losing 3–5 to Marcus Campbell in the quarter-finals.

[96] Williams then suffered a huge dip in form as he lost in the first round of six successive ranking events; after his defeat to Mark King in the 2012 UK Championship he suggested that he was contemplating retirement.

[95] At the 2013 China Open in March Williams won his first match in a ranking event since September with a 5–2 victory against Lü Haotian and continued his run by defeating Ali Carter 5–4, before losing 1–5 to Selby in the quarter-finals.

[95] At the 2013 World Championship he lost 6–10 to debuting compatriot Michael White in the first round and admitted afterwards that the season had been one he would be looking forward to forgetting, but he was committed to playing next year.

[101] He did earn an encouraging 4–3 win over world number one Neil Robertson at the 2014 Welsh Open; Williams said afterwards that he was glad he had ignored his friend Stephen Hendry's advice to retire and believed he still had ranking event titles left in him.

[102] He had chances to move 3–0 ahead in the last 16 against Marco Fu, but eventually lost 2–4; afterwards he said that the Williams who won two world titles over 10 years ago was "dead".

[109] After knocking out Judd Trump 4–1 to reach the quarter-finals of the 2015 Welsh Open, Williams said that he no was longer expecting to win tournaments and was more concerned with improving his ranking.

[111] Williams took advantage of Ben Woollaston missing chances to send their match into a deciding frame after he had been 3–5 behind, but lost it to just fall short of reaching the final in his home tournament.

[113] Despite only being 39 years old, Williams took part in the 2015 World Seniors Championship as he would turn 40 before the end of the season and he won the title by beating Fergal O'Brien 2–1.

[106] After defeating Thepchaiya Un-Nooh in the first round of the Players Championship Grand Final, Williams produced back-to-back comebacks from 1–3 down to knock out both Mark Selby and Matthew Selt 4–3.

[106] He then reached his first major ranking event final in over three years with a 4–2 win over Judd Trump and raced into a 3–0 lead against Joe Perry.

[122] Williams won a trio of frames to force a decider in the semi-finals of the 2016 Riga Masters against Michael Holt, but missed the final brown to be defeated.

[133] Williams qualified for the 2018 German Masters and lost the first two frames of his first-round match against Fergal O'Brien but made a comeback to win 5–3, He then defeated Matthew Selt 5–2 and Jimmy Robertson 5–3 to reach the semi-finals.

The match was described as one of the best finals in the history of the tournament, Williams winning 18–16 to claim his third World Championship making him (aged 43 at the time) the oldest winner since Reardon, who was 45 in 1978.

[137] Following victory, Williams thanked his late sponsor Ron Skinner, who had died two months earlier, his wife for convincing him not to retire, and coach Stephen Feeney for turning his game around so dramatically from a year ago.

[151] At the 2021 World Championships, Williams defeated long-term rival John Higgins 13‍–‍7 in the second round[152] before losing 3‍–‍13 in the quarter-final to Mark Selby.

[153] In August 2021 Williams won his twenty fourth ranking title after defeating Gary Wilson 6‍–‍4 in the final of the British Open.

[161] In October 2023 Williams beat Mark Selby 10‍–‍7 in the final of the British Open in Cheltenham to become the second oldest winner of a ranking event.

[136] He is good friends with fellow snooker professionals Matthew Stevens, Jackson Page and Stephen Hendry, as well as boxer Joe Calzaghe.