Josh Thomson currently works as an analyst and competes in Bellator MMA's lightweight division. A professional competitor since 2001, Thomson has also competed in PRIDE, Strikeforce, UFC, the World Fighting Alliance, and appeared at Dynamite!! 2010. Thomson is a former Strikeforce World Lightweight Champion and a former Strikeforce U.S. Lightweight Champion.

Thomson was born and raised in San Jose, California, growing up in the east side of the city. Being half-European and half-Mexican, Thomson faced discrimination and got into fights often. Thomson moved to Idaho to live with his father where he went to high school and competed in wrestling. Thomson continued wrestling at junior college powerhouse, North Idaho Community College, and also briefly attended Stanford University, but decided the school was not for him after only attending for a few weeks.

Thomson started out very strongly in his MMA career winning his first two professional bouts, before going to a no contest with Kid Yamamoto. Thomson would then go on to win his next three fights, including a win over former WEC Lightweight Champion Rob McCullough.

Thomson made his debut in the UFC at UFC 44 defeating Gerald Strebendt by knockout in the first round. He would then pick up a decision victory over Hermes Franca in an incredible fight at UFC 46, before falling victim in his next fight to a highlight reel KO finish at the hands and foot of Yves Edwards.

Thomson was 2-1 in the UFC and 7-1-1 overall before leaving the UFC and opting instead to go overseas to Japan and fight once for PRIDE FC. He won his single fight in PRIDE by submission in the 1st round. Thomson then signed with Strikeforce and would lose his debut fight (a fight for the vacant Strikeforce Lightweight Championship) to Clay Guida, but would then go on to win his next six fights, including victories over Duane Ludwig and Nam Phan, and would earn another shot at the Strikeforce Lightweight Championship.

In June, 2008, he defeated Gilbert Melendez by unanimous decision at Strikeforce: Melendez vs. Thomson to become the Strikeforce Lightweight Champion.

In December, 2009 at Strikeforce: Evolution, Thomson fought Gilbert Melendez after overcoming a series of injuries for the Lightweight Championship. Thomson would lose the fight by unanimous decision, but the fight would see both fighters put it all on the line in what would prove to be a very fast-paced and exciting fight.

Thomson fought Pat Healy at Strikeforce: Fedor vs. Werdum and won by rear naked choke late in the 3rd round. After this win, Dave Camarillo granted him his black belt in Guerrilla Ju-Jitsu. Thomson broke two ribs during the fight on Healy's very first takedown and fought the rest of the fight very defensively.

Thomson fought Gesias Cavalcante in October, 2010 at Strikeforce: San Jose, where he won by unanimous decision.

Thomson's next fight was against Tatsuya Kawajiri, under the Dream banner, at its end of year event Dynamite!! 2010. He lost the fight via unanimous decision.

Thomson returned in March 2012 and face K.J. Noons at Strikeforce: Tate vs. Rousey. He won the fight via unanimous decision. Thomson once again faced Gilbert Melendez for the Strikeforce Lightweight Championship at Strikeforce: Barnett vs. Cormier on May, 2012. He lost the fight via split decision.

Following the dissolution of Strikeforce in January 2013, Thomson returned to the UFC and faced Nate Diaz in April, 2013 at UFC on Fox 7. He won the fight via TKO, becoming the first fighter to finish Diaz by way of strikes. The win also earned him his first Knockout of the Night bonus award.

Thomson was expected to face current UFC Lightweight Champion Anthony Pettis on December 14, 2013 at UFC on Fox 9, replacing an injured TJ Grant. However, the bout was cancelled after Pettis pulled out of the bout citing a knee injury.

Thomson faced Benson Henderson in January, 2014 in the main event at UFC on Fox 10. Henderson defeated Thomson via split decision. Many media outlets and observers were split on who they thought should have been declared the winner.

During the first round Thomson broke the thumb on his right hand, contributing to his inability to punch with much effectiveness. 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.

Thomson lost in a close fight to Bobby Green at UFC on Fox 12 July 26th, 2014 in San Jose.  It was Thomson's second straight split decision loss.

Thomson was expected to face Gilbert Burns on March 21, 2015 at UFC Fight Night 62, but on February 26, Thomson pulled out of the fight with an undisclosed injury, while Burns remained on the card against a replacement.

Thomson faced Tony Ferguson at UFC Fight Night: Mir vs. Duffee on July 15, 2015.  He lost the fight via unanimous decision and was subsequently released from the UFC.

On August 11, 2015, Thomson signed a multi-fight contract with Bellator MMA.  He made his debut on September 19, 2015 at Bellator MMA & Glory: Dynamite 1 against Mike Bronzoulis, winning via submission in the third round.

Thomson faced Pablo Villaseca on December 4, 2015 at Bellator 147. He won the fight via TKO in the second round.

In his third fight for Bellator MMA Thomson faced Patricky Freire in the main event at Bellator 172 on February 18, 2017. He lost the fight via knockout in the second round.

On January 28, 2020, Thomson announced his retirement from mixed martial arts.