Gera scored 25 goals in 155 appearances during four years with the Baggies before moving to Fulham on a free transfer in 2008.
He has opted against renewing his contract at Craven Cottage in favour of a return to West Brom, who are now managed by his former Fulham boss Roy Hodgson.
The Hungarian has signed a two-year contract, with the option of a further 12 months in the Baggies' favour, and Hodgson is delighted to capture the 32-year-old.