This paper demonstrates the use of topology optimization as a design tool for a thin-shell bridge structure. The presented topology optimization algorithm computes the material distribution within the shell while maximizing its overall stiffness for a given volume of material. The optimization routine is coupled to a Finite Element Method and finds its solution using the Fixed Point Iteration method or Picard Iterations. Besides obtaining the optimal shell thickness distribution, the topology optimization routine also suggests the optimal shape. The optimal shape enhances the mechanical behavior of the structure. The results of this study show that after topology optimization, the deck’s deflection, the shell’s Von Mises stresses, the eigenfrequency of free vibration as well as the deck’s bending moments are improved. This study uses a simplified model of the existing steel shell of the Knokke Footbridge as a case study.