Owen made 110 appearances for the Valiants after turning his initial loan spell at the club into a permanent deal in 2009.
He becomes the second player to leave Vale Park on Tuesday following the departure of midfielder Darren Murphy.
Manager Micky Adams told the club's official website: "Gareth has been an absolutely terrific servant for this football club and we wish him every success as he moves on.
"I am sure that he and the club will have some fantastic memories of his time at Vale Park."
Owen added: "I leave Port Vale with a heavy heart and I'd like to thank everyone who has supported me during my time at the club.
"I've thoroughly enjoyed my time in Burslem and will be keeping a close eye on results between now and the end of the season - I really hope that the boys can push on and achieve promotion."