The loss of composite action at the negative moment region for a continuous composite girder reduces the girder’s strength and stiffness. This paper presents an experimental investigation into the use of carbon fiber–reinforced polymer (CFRP) to maintain the composite action at the negative moment region of continuous composite girders. This is achieved by bonding CFRP sheets to the top of a concrete slab at the negative moment region. Six two-span continuous composite girders were tested. CFRP sheet thickness was varied to assess its effect on girder behavior. The girders were designed to have full composite action between the concrete slab and the steel girder. Moment capacity at the positive and negative moment regions was evaluated experimentally and theoretically. A plastic analysis was conducted to evaluate the ultimate capacity of the girders. Finite-element modeling evaluated girder performance numerically. The experimental results confirmed the effectiveness of CFRP sheets in maintaining composite action at the negative moment region and in preventing crack initiation in a concrete slab under service load. The use of CFRP improved the strength and stiffness of the continuous composite girders. The plastic analysis safely estimated the girders’ ultimate capacity. The developed finite-element model yielded satisfactory results.