Gera, 30, suffered a cruciate ligament injury in January and his deal expired at the end of June.
He has continued to work with the medical team at the Baggies throughout the summer and, expected to resume full training a week on Monday, they have handed him a one-year deal.
“It’s great to have Zoltan on board for another season,” said manager Steve Clarke. “He’s a top professional and good within the group.
“I believe his form last season before his injury was as good as at any time in his career and our main aim is to get him back to that level as quickly as possible.
“If he reaches that level again, he will be a great asset for us.”
The 34-year-old Hungary midfielder, who has 74 international caps, returned from a similar injury at the start of last season.
Having originally joined in 2004, he left the club in 2008 for Fulham but returned to The Hawthorns in 2011.