King turned professional in 1991 and advanced steadily through the rankings, reaching the top 48 by 1996. His
Welsh Open final run led to a top 32 place in the end of season rankings, and he continued to progress by reaching the top 16 a year later. He made his debut at the
World Snooker Championship in
1994, losing to
Darren Morgan in the first round. He remained in the top 16 the following season without reaching a ranking quarter-final, but dropped out a year later. He made an immediate return in
2000–01, climbing to a career-high of #11. A poor
2002–03 season ended with him dropping out of the top 16 again after defeat to
Drew Henry 10–5 in the first round of the World Championship. In the post-match interview, King suggested that he had lost patience with the game and would quit because "I've just had enough of the game." After the
2004 World Championship, King became involved in a tense battle with
Quinten Hann after his friend
Andy Hicks eliminated Hann in a controversial first-round clash. Hann had been making provocative gestures during the match and after Hicks took victory, the two players had an altercation, with an angry Hann squaring up to Hicks. Upset by Hann's behaviour, King challenged the Australian to a boxing match, for which King was later criticised, as Hann's behaviour had already put the game into disrepute. Nevertheless, the bout went ahead and Hann controversially won the fight on a points decision. In December 2004, King beat
Robin Hull,
Mark Williams,
Alan McManus and
John Parrott en route to the semi-finals of the
UK Championship, losing 9–4 to eventual winner
Stephen Maguire. At 8–3, a mobile phone went off in the crowd, prompting King to quip "if that's my missus, tell her I'll be home soon". In 2005, King beat
Ronnie O'Sullivan 9–8 at the same event, having fought back from 5–3 down in a match which saw his opponent sitting with a wet towel draped over his head when King was at the table. King would eventually lose 9–6 in the last 16 to
Joe Perry, but made a career best 146 break at the 2006 Championships. Defeat to
Neil Robertson (he was trailing 7–2 but only lost 10–9) in the qualifying for the
World Championship in 2005 cost him the chance of a top 16 return, but King qualified a year later, resiliently losing 10–6 to Stephen Maguire in the first round. In 2007, King went out to
David Gilbert in the qualifying round for the event. In the
2008 World Championship, King beat six-times runner-up
Jimmy White to qualify, then shocked the previous year's runner-up
Mark Selby 10–8, having trailed 5–3 overnight. After potting the match ball, King showed his delight by shouting "Get in". He lost to
Peter Ebdon in the last 16, but his top-16 place was secure and he would start the 08/09 campaign ranked 15th. A consistent
2008–09 season saw King retain his top 16 spot. At the
2009 Grand Prix King needed three snookers in the deciding frame against
Ricky Walden to claim a 5–4 victory. He managed to get them and won by potting the final black. In the next round he lost to
Robert Milkins. At the
2010 China Open King defeated Thai player
James Wattana 5–4 in the first round after trailing 2–4. He then won his second match 5–3 against Chinese player Tian Pengfei to reach his first Quarter final since the 2007 Malta Cup. A double triumph for King, the win helped to maintain his Top 16 place for the 2010/11 season. At the
2010 World championship, King lost his first round match against former 6 times World Champion
Steve Davis by 9–10. In the deciding frame, Davis led 55–37, with only 13 points available. King's attempts at getting the snooker he needed to win ended with him fluking the pink in the pocket. King made an impressive start to the new season when he reached the Quarter Final of the
2010 Shanghai Masters. King was too strong for qualifier Joe Delaney in the first round, winning 5–3. The same scoreline saw him overcome Peter Ebdon in the next round but King was then beaten comfortably by Mark Selby 5–1. However his lack of form in the following ranking events made him fall out of the top 16 after the
2011 Welsh Open. At the
2011 Masters, King beat defending champion Mark Selby 6–4 to reach his first quarter-final at the event since 1999. After the match, King suggested that his comeback from 0–2 down was prompted by his opponent's celebration to winning the second frame on the black, when he "put his cue up and it gave me the hump a bit" King then lost in the quarter-finals 1–6 against
Jamie Cope. He ended the season by losing 7–10 to
Graeme Dott in the
World Championship and was ranked 26, dropping 11 places during the year. He was therefore out of the top 16 in the end of season rankings for the first time since the
2007–08 season.
2011/2012 season King's ranking meant that he would need to win a match to qualify for the ranking tournaments in the
2011–12 season. He failed to qualify for four of the eight ranking tournaments during the season and was knocked out in the first round in two. However, he produced an excellent run in the
Shanghai Masters where he reached his first semi-final since the
2005 Welsh Open. He required a final frame decider to beat
Liu Song in qualifying 5–4 and once in
China he won by the same scoreline to knock out defending champion
Ali Carter in the first round. Further wins followed over
Fergal O'Brien and
Anthony Hamilton, before he was whitewashed 0–6 by
Mark Selby in the last four. King also reached the quarter-finals of the
World Open by beating
Mark Williams 5–1 and
Tom Ford 5–4, but then lost 1–5 to
Mark Allen. King lost to seventeen-year-old
Luca Brecel in qualifying for the
World Championship and finished the season ranked world number 31, dropping five places during the year.
2012/2013 season King began the
2012–13 season by failing to qualify for three of the first four ranking events. The one he did reach was the
Shanghai Masters, where he beat Zhao Xintong 5–3 in the wildcard round and local favourite
Ding Junhui 5–4 in the first round, having trailed 0–3. He lost 3–5 to
Shaun Murphy in the following round. King defeated
Mark Williams 6–3 in the first round of the
2012 UK Championship, before surrendering a 3–0 lead against 17-year-old
Luca Brecel to lose 4–6. He also reached the second round of the
German Masters by whitewashing
Stephen Maguire 5–0, but then lost in a deciding frame to
Matthew Stevens. He raced into a 6–2 lead in the first session of his second round match against
Ding Junhui, before falling 7–9 behind in the next session and ultimately lost 9–13. King ended the season ranked world number 29.
2013/2014 season King had his best results in the Chinese ranking events during the
2013–14 season, beginning with the
Wuxi Classic where he beat
Rory McLeod 5–3 and
Marco Fu 5–4, before being thrashed 5–0 by
Neil Robertson in the last 16. At the
Shanghai Masters he knocked out
Graeme Dott, but Robertson was again victorious when the pair met in the last 16 this time winning 5–3. During King's tie with
Fergal O'Brien in the last 64 of the
2013 UK Championship, he made 15 consecutive foul and misses in the sixth frame and went on to lose 6–3. At the
China Open, King saw off
Aditya Mehta 5–4, Fu 5–3 and
Jamie O'Neill 5–3 to reach his only quarter-final of the season. King failed to reach
The Crucible this year as
Jamie Cope beat him 10–7 in the final round of
World Championship qualifiers.
2014/2015 season King lost in the qualifying rounds of three of the first five ranking events of the
2014–15 season and was knocked out in the first round of the other two. He defeated
Steven Hallworth and
Michael White both 5–3 to qualify for the
German Masters and eliminated world number five
Barry Hawkins 5–3 in the first round. In the last 16 he lost 5–2 to
Stephen Maguire. A consistent season in the
European Tour events saw King finish 24th on the
Order of Merit to make his debut in the
Grand Final. King secured another win over Hawkins this time 4–2 and looked like moving 3–2 ahead of
Judd Trump in the last 16. However, Trump got the snooker he needed and won the next frame to defeat King. King closed the season with a 5–4 loss to
Robin Hull in the second round of the
China Open and was narrowly edged out 10–9 by
Anthony McGill in the final round of
World Championship qualifying.
2015/2016 season King was knocked out in the first round of the
2015 Australian Goldfields Open 5–1 by
Mark Selby. At the
Paul Hunter Classic, King advanced to the semi-finals with the loss of just one frame. He moved 3–0 up on
Shaun Murphy with two 123 breaks but then missed multiple chances to win the match, as well as Murphy getting some flukes, to be beaten 4–3. He was also a losing quarter-finalist at the
Gibraltar Open and
Gdynia Open to finish ninth on the
Order of Merit. In the
Grand Final he lost 4–2 to
Mark Allen in the second round. He could not win a frame after being 3–2 up on
Judd Trump to lose 5–3.
2016/2017 season – first ranking title King failed to get past the second round in the first eight events of the
2016–17 season. At the inaugural
Northern Ireland Open, King beat
Igor Figueiredo,
Liang Wenbo,
Fergal O'Brien,
Kurt Maflin,
Hossein Vafaei Ayouri and
Kyren Wilson to reach his first ranking event final since 2004. He was 5–1 down to
Barry Hawkins, before winning six successive frames. King went on to be 8–7 up, with the 16th frame going to a re-spotted black after King had needed a snooker and he missed a double on it to win. King took the deciding frame to win a ranking event for the first time in his 25-year career. He paid tribute to his father who had lent King money for the trip to Belfast. King defeated
Stephen Maguire and
Ali Carter both 4–3 to progress to the quarter-finals of the
World Grand Prix, where he lost 4–2 to
Marco Fu. For the fourth year in a row King could not play in the
World Championship as he was beaten 10–4 by
Xiao Guodong in the final qualifying round. ==Betting ban==