Pennant's deal included a clause that would have allowed the club to keep him until the end of the season, but he has been allowed to pursue other options.
The 31-year-old moved to the Britannia Stadium in 2010 but struggled to make an impact, earning just 45 Premier League starts, and none this season under Mark Hughes.
"I met with the manager and he was honest with me which I appreciated, I wasn't playing and at 31 now I need to be playing games," Pennant told TheMirror.
"I'd like to thank the club for the opportunity of a new challenge and would like to thank everyone at Stoke City and the fans for the fantastic support over the last few years.
"I'm looking forward to the new chapter in my life."
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