The 34-year-old Serbian striker, who was released by Blues in the summer, has signed a deal that will keep him at St Andrews for the remainder of the season.
Zigic will be not available for first team selection until next weekend, 13th December, when visa requirements are expected to be completed.
"We are delighted to have agreed a deal with Nikola and secured a work permit,” club director Panos Pavlakis told the official Blues website.
"With Nikola's signing, following those of Michael Morrison and Guy Moussi, our fans can rest assured that we are doing everything we can to support Gary and strengthen the team even more. That has to be the focus."