Josh made his return at UFC 82, defeating Dustin Hazelett by TKO due to strikes at 1:24 of the 2nd round.

Koscheck was to fight Chris Wilson at UFC 98 but was forced to withdraw after suffering a foot injury in training. He returned at UFC 103 and defeated returning veteran Frank Trigg via TKO (punches) in the 1st round.

Josh Koscheck began wrestling when he was five years old. He had been having a pause from sport since he was twelve but began it again when he became a teenager and became successful in collegiate wrestling, dating back to his years at Edinboro University of Pennsylvania, where he attended the university on an athletic scholarship. In 2001, during his Junior season, Koscheck won all of his wrestling matches and went on to become the NCAA Division I Champion in the 174 lb weight class. In addition to being a four-time NCAA Division I All-American (placing 4th, 2nd, 1st and 3rd respectively), Koscheck is a three-time recipient of the PSAC Wrestler of the Year award and earned the Eastern Wrestling League Achievement Award twice. Koscheck earned a bachelor's degree in Criminal justice from Edinboro University. Koscheck spent a few months coaching at Erie Cathedral Prep and one and a half years as the assistant head wrestling coach at the University at Buffalo.

Koscheck appeared on the first season of The Ultimate Fighter as a middleweight fighter. He defeated Chris Leben via unanimous decision to advance to the semifinals, where he was defeated by Diego Sanchez via split decision. Koscheck had his first official UFC fight on April 9, 2005, at The Ultimate Finale, where he defeated Chris Sanford with a first-round KO. Koscheck followed this victory with another win at Ultimate Fight Night over UFC veteran Pete Spratt in Koscheck's debut at welterweight. Since then, Koscheck has amassed an additional three victories after experiencing his first career loss to Drew Fickett due to a rear naked choke. Koscheck then defeated Canadian welterweight standout Jonathan Goulet at UFC Fight Night 6 by submission due to strikes.

Koscheck's fight on December 13, 2006 was against Brazilian Jiu-Jitsu black belt Jeff Joslin at UFC Fight Night 7 where he won by unanimous decision.

On August 25, 2007, Koscheck was defeated by Georges St-Pierre at UFC 74 via unanimous decision (30–27, 29–28, 29–28). St-Pierre's wrestling skills were displayed during the match by outwrestling Koscheck, scoring takedowns, stuffing Koscheck's takedown attempts and maintaining top position throughout most of the fight. There was speculation before the fight that Koscheck would out-match St-Pierre on the ground due to his credentials, but St-Pierre was confident that he was a better Wrestler and striker and was more well versed in submissions than Koscheck.

On December 10, 2008, Koscheck fought Yoshiyuki Yoshida in the main event at UFC: Fight for the Troops and won by KO in the first round by landing two devastating straight right punches to Yoshida's head. The Japanese fighter remained on the canvas, while being tended to by commission doctors and was removed from the Octagon on a stretcher as a precautionary measure. He was later treated and released from a local hospital for a concussion. Koscheck received $60,000 bonus from the UFC for Knockout of the Night.

On November 21, 2009, Koscheck defeated Anthony Johnson by rear naked choke at 4:47 in the 2nd round. In the first round, Koscheck blocked a knee aimed at his head while he had two knees on the ground. Koscheck went to the ground holding his face, prompting the Referee to step in and deduct a point from Johnson. Commentators accused Koscheck of faking the impact of the knee, which seemed to miss Koscheck's face on the replays. Koscheck has said in multiple interviews that he was reacting to an eye poke, not the knee. In round two, Koscheck poked Johnson in the eye twice leading to Johnson being given time to recover. Because of this, many fans think due to the controversy in both rounds between the fighters, it should've been declared a No Contest. In his post fight interview, he called out Dan Hardy, the #1 contender in the Welterweight Division.

In 2010, Koscheck was a coach on The Ultimate Fighter season 12. The season 12 finale aired on December 4, 2010 with the main event consisting of two fighters (Michael Johnson and Jonathan Brookins) from team Georges St-Pierre.

Koscheck defeated former UFC welterweight champion Matt Hughes on September 24, 2011 at UFC 135 via KO in the first round, replacing an injured Diego Sanchez.

Koscheck was expected to face Jake Ellenberger on September 1, 2012 at UFC 151. However, Koscheck pulled out of the bout citing a back injury.

Koscheck next faced Tyron Woodley at UFC 167 on November 16, 2013. He lost the fight via knockout in the first round.

On June 26, 2015, it was announced that Koscheck signed a multi-year deal with Bellator MMA. Koscheck was set to make his debut against Fellow welterweight Matthew Secor on January 29, 2016 in his home town of Fresno California and was set to also be the main event.

It was announced on January 31, 2017, that Koscheck's previously delayed Bellator debut would take place at Bellator 172 on February 18, 2017 against Mauricio Alonso. He lost the fight via TKO in the first round.