Between 2000 and 2004 Liam established himself as the top fighter in the United Kingdom in his weight class, having moved up from
featherweight (52 kg/114.4 lbs) to
light welterweight (63.5 kg/139.7 lbs) and having beaten domestic and international competition including Ait Said Aberderahman, Preechapon Por Nuongubon, Satoruvasikoba. At the end of 2004 Harrison travelled to Italy where he was supposed to face reigning champion Massimo Rizzoli for his
W.A.K.O. low-kick kickboxing world title. Rizzoli suffered an injury and Liam faced the W.A.K.O. European champion Emannuel Di Profetis instead. Despite the late change of opponent and fighting in a rule set different from
Muay Thai, Harrison won the match by
technical knockout to become world champion. The win in Italy was followed by success at home when Harrison defeated Dutch-based kickboxer Mohamed Ajuou to claim the European version of the S.I.M.T.A. belt. In following fights Harrison beat Abdoulaye M'baye and Benzouaoua Hakim as well as Hiromasa Masuda in a rematch from 2003 and was still undefeated into 2005. He made his Thai debut in August of that year, losing a
split decision to Witthayanoi Sitkuanem at
Rajadamnern Stadium in what was the first defeat of his pro career. Harrison suffered a second consecutive loss a few months later on his return to England, losing to another Thai in Duwao Kongudom who was a highly rated Omnoi Stadium champion, in a match in
Wolverhampton. Despite suffering two defeats including losing his Thai debut Harrison headed back to
Thailand at the end of 2005. He won his first title on Thai soil by defeating a much bigger Russian opponent to claim the Patong Stadium belt at 68 kg (149.6 lbs). With his first victory in Thailand, Liam strung together five more victories in the country throughout 2006 which included winning the W.P.M.F. light welterweight belt against reigning champion Masa Hiroshima as well as retaining his Patong stadium title. He also re-matched Witthayanoi Sitkuanem but was once again unsuccessful. That year was awarded the "Leeds Sports Federation Sportsman of the Year" award. Throughout 2007 Liam fought primarily in Thailand, basing himself at the Jitti Gym in Bangkok. He fought a number of bouts at the major stadiums including at
Lumpinee Stadium, managing to successful defend his W.P.M.F. world title two times that year. He also made brief forays back to the United Kingdom, facing W.M.C. world champion Numphon PK Sterio two times that year. Liam lost the first match between the pair, but won the second in Manchester in November via a fourth-round KO, picking up his biggest victory up to that point as well as winning the W.M.C. lightweight world title. He was also named as the Muay Siam magazine's top foreign fighter of the year. In 2008 Harrison fought a number of bouts at Bad Company promoted shows in his home town of Leeds, with wins over Benabdeljelil Mehdi and Masaru Ito. He also retained his W.M.C. lightweight world title by stopping Sarmsamut Kiatchongkao in June of that year. In 2009 Harrison lost a decision to
Saenchai Sor Kingstar in London. He then headed to Jamaica to face
Anuwat Kaewsamrit, being defeated via
TKO and losing his W.M.C. world title in what was his first ever stoppage loss. Harrison would gain revenge against
Anuwat Kaewsamrit in March 2010, defeating him by
unanimous decision over five rounds in their rematch in Manchester. Although Anuwat was not at his peak anymore he was Harrison's best victory up to date. He would also have the chance to enhance his name by entering the inaugural Thai Fight competition, an event involving sixteen Muay Thai fighters at 67
kg/147.4
lbs with a first place prize of 2,000,000
Baht (around $62,000). Despite being one of the smaller fighters at the tournament he outworked Behzad Rafigh Doust in his first match forcing him to quit in the second round. Going into the quarter-finals Liam then knocked out Soishiro Miyakoshi with elbows. Harrison was later disqualified from the tournament for coming in over the weight. He insisted it being the result of a sickness he caught prior to the match. In 2011 Harrison had two rematches against opponents who had defeated him in the past. He lost both of them, against
Saenchai Sor Kingstar and Petaswin Seatranferry, who had defeated him at an event in
Glasgow the previous year. On 31 March 2012 he beat
Andrei Kulebin by TKO in round 3 using his kicks. Harrison lost to
Saenchai PKSaenchaimuaythaigym for the third time at
Muay Thai Warriors in
Macau on 9 December 2012, losing a clear-cut unanimous decision. He competed in the
Glory 8: Tokyo - 2013 65 kg Slam in Tokyo, Japan on 3 May 2013. He lost to
Masaaki Noiri via TKO due to a cut in round two in the quarter-finals. He lost to
Sagetdao Petpayathai by decision in the semi-finals of a four-man 68 kg tournament at
MAX Muay Thai 3 in Zhengzhou, China on 10 August 2013. Harrison stopped his four-fight losing streak with a unanimous decision victory over
Dylan Salvador at
The Main Event 2013 in Manchester, England on 2 November 2013. He was set to fight
Damien Alamos for his
Yokkao promotional debut at
Yokkao 8 in Bolton, England on 8 March 2014 but Alamos withdrew from the fight, claiming to have a hand injury, and was replaced by
Houcine Bennoui. He defeated Bennoui on points in a five-round −65 kg Muay Thai bout. Harrison defended his Yokkao 65 kg title on 25 March 2017 at Yokkao 24 against Ryan Mekki. On 8 March 2025 Harrison claimed the
WBC Diamond Belt after defeating Spain's Isaac Araya. Harrison holds notable wins over
Muangthai P.K.Saenchai,
Tetsuya Yamato,
Malaipet Sasiprapa,
Andrei Kulebin,
Anuwat Kaewsamrit, and
Dzhabar Askerov.
ONE Championship In 2018, Harrison linked a non-exclusive deal with
ONE Championship to compete in ONE Super Series Muay Thai. He lost his first two bouts to
Petchmorakot Petchyindee Academy at
ONE: Destiny of Champions and
Rodlek at
ONE: Legendary Quest, but won by first-round KO in his third bout with the organization at
ONE: A New Tomorrow against Mohammed Bin Mahmoud. Harrison faced
Muangthai P.K.Saenchai at
ONE 156 on 22 April 2022. He won the fight by a first-round technical knockout. Harrison was awarded a $100,000 bonus for winning the fight. Harrison faced
Nong-O Gaiyanghadao for the
ONE Bantamweight Muay Thai World Championship at
ONE on Prime Video 1 on 27 August 2022. He lost the bout in the first round after being unable to continue due to leg kicks. Harrison was scheduled to face
Pongsiri P.K.Saenchai on 14 January 2023, at
ONE Fight Night 6. However, Harrison withdrew from the event due to injuries and requiring surgery. As a result, the bout was scrapped. Harrison was scheduled to fight former unified multiple division champion
Floyd Mayweather Jr. in an exhibition bout, but pulled out. After a 16-month and 14-day hiatus due to injury, Harrison was scheduled to face
John Lineker on 13 January 2024, at
ONE Fight Night 18. However, Harrison suffered a knee injury and the bout was scrapped. Harrison was scheduled to face Katsuki Kitano on 8 June 2024, at
ONE 167. However, the bout was removed from the event after both fighters missed weight. Harrison faced
Saeksan Or. Kwanmuang on 6 September 2024, at
ONE 168. He lost the bout via technical knockout after being knocked down three times, and appeared to be retiring after the bout by laying his gloves on the canvas. Harrison returned from retirement against Isaac Araya for the WBC Muay Thai Diamond title on 8 March 2025, at Hitman Fight League 7. He won the title via technical knockout in round three. Harrison is scheduled to face
Soe Lin Oo on 1 August 2025, at
ONE 173. In 2019, Harrison said that he would fight anyone under
Lethwei rules. Which prompted Lethwei world champion
Dave Leduc to offer US$10,000 to a charity in
Myanmar if Harrison would to fight Soe Lin Oo in a Lethwei fight at
World Lethwei Championship, but the fight never materialized. == Titles and accomplishments ==