April 16, 1966|
A physiotherapist by profession, Shamsul gave up his practice to become a full time member of the Football Association of Singapore (FAS) in his role as referee's executive. Since becoming a referee on 1 January 1996, he has won both the 2005 and 2006 Asian Football Confederation Official of the year, becoming the first Singaporean to achieve this refereeing honour. He has also won the S.League Referee Of The Year award four times, in 1997, 1998, 1999 and 2001. He announced retirement in 2007 and in 2008 started to work with FIFA, first referee from Southeast Asia, as referee instructor.
He is currently a FIFA Referee Instructor, an AFC Elite Referee Assessor and Recruiter and member of the FAS Referees Committee.
International tournaments 
Shamsul Maidin has officiated in the 1996, 2000 and 2004 AFC Asian Cups, as well as the 2001 and 2003 FIFA World Youth Championship, 2005 FIFA Confederations Cup and 2006 FIFA World Cup. He was also the only non-African referee at the 2006 African Cup of Nations.
2010 FIFA World Cup 
In the 2010 World Cup at South Africa, Shamsul was appointed by FIFA to the referees committee.
2006 FIFA World Cup 
In 2006, Shamsul was selected by FIFA to be one of the official referees at the 2006 FIFA World Cup in Germany, only the second time a Singaporean had taken part in a FIFA World Cup in a designation of Official Referee, after George Suppiah in 1974, also held in Germany (then West Germany).
He took charge of the group stage game between Trinidad and Tobago and Sweden, brandishing the first red card of the tournament to Trinidad and Tobago's Avery John. He also took charge of the group stage game between Mexico and Angola, sending off Angola's André Macanga, becoming the first referee at the tournament to produce two red cards. By taking charge of the Mexico–Angola match, Shamsul also became the first Singaporean to referee more than one match at a World Cup Finals.
He was also in charge of the final Group A game between Poland and Costa Rica, making him the first referee to officiate 3 games in the FIFA World Cup 2006, and was appointed fourth official for the round of 16 match between Germany and Sweden.
He was however not one of the 12 referees to officiate the quarter-final matches onwards as he was sent home along with 14 other referees despite giving one of the most consistent performances  and escaping the scrutiny of the press which his fellow referees such as Valentin Ivanov and Graham Poll suffered from.
2005 Confederations Cup 
In addition, during the 2005 FIFA Confederations Cup, he officiated in the Argentina v Australia match in Nuremberg, in which Argentina won 4–2. The Australian media then blamed Shamsul for Australia's defeat as he denied Australia a penalty after substitute striker Mark Viduka was allegedly brought down by Fabricio Coloccini.