Josh joined Brentford in the summer of 2011, having been spotted playing park football. He progressed from the youth team to the Development Squad and signed a one-year professional contract for the 2013–14 season. His debut came during a 5–0 League Cup second round defeat at Derby County in August 2013. With promotion to the Sky Bet Championship secured, he made his league debut on the penultimate day of the season at Colchester United.

Josh didn’t feature during the 2014/15 season but made 12 appearances in all competitions for The Bees the following campaign, either side of ten appearances during a loan spell with Barnet. After a strong finish to the campaign he carried on where he left off the next season, netting his first Brentford goal during a 4-1 victory over Reading in September and opening the scoring at Loftus Road the following month, as we ended a 52-year-wait for a win in W12. He would go on to make 32 appearances for the Club in all competitions, the same number as he would manage during the 2017/18 season.

His performances during the first half of that season, which included another goal at Loftus Road, this time in a 4-1 EFL Cup victory, were recognised with a nomination for the EFL Player of the Year at the London Football Awards. Since then the 24-year-old has featured just five times for the First Team, spending the second half of last season on loan at Burton Albion. In total, Josh leaves TW8 having scored five goals in 84 appearances.

Phil Giles, Brentford FC Co-Director of Football, said: "Josh Clarke has been a stalwart of Brentford FC for many years now, he has been ready when needed and played some very good games, most memorably at Loftus Road. We felt that with the prospect of regular minutes for our First Team during the rest of the season quite unlikely, and in the absence of a club with a vacancy at the end of this transfer window, the best thing for everyone was that Josh terminated his contract prior to the end of the window. This means that he is free to sign for a new club immediately. We wish him every success in his future career."