Prior to competing in ONE Championship, Wiratchai began his career at DARE Championship–at the time the only MMA promotion in Thailand–held at Club Insomnia in Bangkok from 2011 to 2012, where he went an undefeated 2–0.

[8] After a period of inactivity the entirety of 2014, Shannon Wiratchai made his return on May 22, 2015 at ONE Championship: Warrior's Quest, where he faced Amir Khan.

[9] He then picked up his first submission win with a rear naked choke victory over Kyal Linn Aung in the first round at ONE Championship: Kingdom of Champions on May 27, 2016.

[11] At ONE Championship: Warrior Kingdom on March 11, 2017, Shannon Wiratchai defeated Richard Corminal by first-round knockout in his Lightweight debut.

[16] In what would be the biggest fight of his career, Wiratchai faced former ONE Lightweight World Champion Shinya Aoki at ONE Championship: Reign of Kings on July 27, 2018.

He would be handed the first submission loss of his career via rear naked choke against Iuri Lapicus at ONE Championship: Enter the Dragon on May 17, 2019.

[18] Shannon Wiratchai faced former ONE Featherweight World Champion Honorio Banario at ONE Championship: King of the Jungle on February 28, 2020.

[22][23] Wiratchai faced former Muay Thai world champion Fabio Pinca, who will be making his mixed martial arts debut, at ONE Championship: No Surrender 3 on August 21, 2020.

Wiratchai has termed his own fighting style the "OneShin Striking System", which is based on "attacking opponents who leave themselves vulnerable".

When he turned pro in MMA, he later applied elements of Brazilian jiu-jitsu, Muay Thai, boxing and wrestling into his style.

On September 9, 2017, Shannon Wiratchai hosted the "OneShin Cup",[37] an amateur mixed martial arts tournament.

Wiratchai created the tournament with purpose of establishing more awareness surrounding the sport of MMA in Thailand, as well as developing Thai mixed martial artists so that they would be capable of competing at an international level.

[43] Until 2019, Shannon Wiratchai had been dating Tiger Muay Thai teammate and fellow mixed martial artist Rika Ishige, who competes in ONE Championship's atomweight division.