The firm - founded by ex-Blackburn Rovers player Dave Whelan - joins Asda and Costco at the Leckwith site.
The JJB development will be similar to the firm's base at the Cyfarthfa Retail Park, in Merthyr Tydfil, which has a fitness centre, including a gymnasium and swimming pool on site, as well as a sports goods store.
Developer Paul Guy said: 'JJB's decision to sign up is very good news. We are also very close to signing up two other tenants. One is going to a board meeting for confirmation this month, while another agreement is with solicitors.'
CLICK HERE FOR FULL STORY