The former West Ham United scholar made just two appearances for the Bees finding first-team opportunities hard to come by due to the impressive performances of Graham Stack.
Cowler released a brief statement on Twitter wishing the best of luck to the players ahead of the new season whilst explaining his desire to leave to play regular football.
“My last day as a @BarnetFC player. Was a difficult decision to make but at the end of the day as a footballer I want to play games…”
He added: “I thank the club for respecting my decision. Some brilliant people at the club and I wish all the players the success they deserve.”