The 31-year-old Scotland international forward has joined City on a one month emergency loan deal.
"We're delighted to be able to bring Chris in," City boss Gary Johnson told the clubs official website.
"He will add vital experience to our strike-force and he'll provide a presence up top as well.
"We've managed to bring him here for a month initially and we'll take it from there."
Iwelumo is expected to make his City debut in the away game at Sheffield United .