WBC world champion

Starting as an amateur in high school, Sirimongkol quickly ascended in professional boxing. He claimed the WBU Super flyweight and Bantamweight titles in 1995 and became the WBC Bantamweight Champion in August 1996 at just 19 years old, defeating interim champion José Luis Bueno in Phitsanulok, Thailand. His title shot was earned through a victory over veteran Thai boxer Thanomsak Sithbaobay.

Sirimongkol successfully defended his WBC bantamweight title three times. However, his reign ended in November 1997 when he lost to former Japanese world champion Joichiro Tatsuyoshi in Osaka, Japan. He rebounded strongly, capturing the WBC Super featherweight title in 2002 with a knockout win over Kengo Nagashima, but lost the title a year later to Jesús Chávez.

Post-world title reign

In May 2007, Sirimongkol won the Asian Boxing Council (ABCO) super featherweight title. He then won the PABA light welterweight title in December 2007 before defending the title once in May 2008.

Arrest and later career

In 2009, Sirimongkol's career took a turn following his arrest for possession of Ya ba. During his incarceration, he taught boxing to fellow inmates and continued to compete, winning the WBC Asia Continental Welterweight title. He successfully defended the WBC Asia Continental belt five times from 2012 to 2014. He was pardoned four years into a 20-year sentence.

In October 2014, Sirimongkol defeated Dan Nazareno Jr. to win the WBO Asia Pacific junior middleweight title. He defended the WBO Asia Pacific belt twice in April 2015 and September 2015.

His 51-fight winning streak was finally broken in 2017 by Uzbek boxer Azizbek Abdugofurov in an unsuccessful bid for the WBC Asia middleweight title, marking his first defeat in 14 years.^[1]

After winning the UBO Inter-Continental light middleweight title in May 2017 and the Thai light heavyweight title September 2018, Sirimongkol announced his first retirement from boxing on September 20, 2018.^[2] He came out of retirement for two more fights, including unsuccessfully challenging Teerachai Sithmorseng for the WBA Asia light heavyweight title in April 2021, before retiring once again.

Bare-knuckle boxing

Sirimongkol made his bare-knuckle boxing debut at BKFC Thailand 1: The Game Changer on December 18, 2021, fighting under his real name of "Sirimongkol Iamthuam". His opponent was Iranian Brazilian jiu-jitsu and full contact karate practitioner Reza Goodary. Despite standing 168 cm and Goodary standing 195 cm, Sirimongkol controlled the majority of the fight and scored a knockdown to win via split decision.^[3][4]