A professional competitor since 2001, Thomson has competed in Bellator MMA, PRIDE, Strikeforce, UFC, the World Fighting Alliance, and appeared at Dynamite!!

Thomson was born and raised in San Jose, California, growing up in the east side of the city.

In middle school, he was involved in a brawl in which the principal was punched while trying to break up the incident, resulting in Thomson being placed in a juvenile hall.

[8] Thomson started out very strongly in his MMA career winning his first two professional bouts, before going to a no contest with Norifumi Yamamoto.

Thomson would go on to win his next six fights, including victories over Duane Ludwig and Nam Phan earning him another shot at the Strikeforce Lightweight Championship.

On November 21, 2008, Thomson was scheduled to make his first title defense in a rematch against Yves Edwards at Strikeforce: Destruction but had to pull out after tearing ligaments in his toe.

Thomson fought Pat Healy at Strikeforce: Fedor vs. Werdum and won by rear naked choke late in the 3rd round.

Thomson fought Gesias Cavalcante on October 9, 2010, at Strikeforce: San Jose where he won a controversial unanimous decision (29–28, 29–28, and 30–27).

[14] Thomson's next fight was against Tatsuya Kawajiri under the co-promoted DREAM, K-1 end of year event Dynamite!!

Thomson was expected to face promotional newcomer Maximo Blanco at Strikeforce World Grand Prix: Barnett vs. Kharitonov but yet another foot injury forced him out of the bout.

[18] He won the fight via TKO (head kick and punches), becoming the first of only three fighters (Hermes Franca & Jorge Masvidal) to finish Diaz.

[28] Disappointed in the result of the Henderson bout, Thomson indicated in the post-fight press conference, that he may be "done" with the UFC or fighting.

[33] However, on February 26, Thomson pulled out of the fight with an undisclosed injury, while Burns remained on the card against a replacement.

[37] He made his debut on September 19, 2015, at Bellator MMA & Glory: Dynamite 1 against Mike Bronzoulis, winning via submission in the third round.