The 33-year-old former West Brom and Bolton left-back has penned a short-term deal following a trial period with the midlands club.
Robinson, a free agent following his release by the Trotters in the summer, arrives with Blues light in numbers in defence following injuries to David Murphy, Paul Caddis, Stephen Carr and Pablo Ibanez.
Manager Lee Clark told Birmingham's official website: "I'd like to thank the board for allowing me to bring in Paul, an experienced defender who will enhance our playing squad.
"While I have been impressed with the progress of our young defenders, recent injuries had left us with just two fit senior defenders so the acquisition of Paul was one we needed to make. As a senior professional, Paul will give us that added experience which is always useful in this competitive division."
Robinson will remain with Blues until Friday October 26.
- Paul Caddis