Vignal, 28, has signed a one-year deal at St Andrew's with a 12-month option after leaving Lens.
Blues boss Alex McLeish, who worked with Vignal during his time in charge of Rangers, has moved for the Frenchman to cover the problematic left-back spot with David Murphy currently sidelined through injury.
"He's a good athlete, he's mobile and he's strong and aggressive," McLeish told the club's official website.
"He played a season with me at Rangers when we won the league and it was a very successful campaign for him then, so I know what Greg can bring us.
"I've kept in touch with him and his family and I know he's been bursting over the last couple of years to get back to the top league."