Howard had been available after being released by Portsmouth last month and Bristol City boss Sean O'Driscoll was delighted to sign the former Barnsley man.
O'Driscoll told the club's official website: "He's got Championship experience and technically, he is very good.
"Brian was available and financially fits into the model going forward. His personality will add something positive to the group."
Howard could go straight into the Bristol City squad to face Cardiff City on Saturday.