This study experimentally investigates the structural behavior of steel–concrete composite beams containing large circular web openings under monotonic four-point bending. The objective is to evaluate how the presence, number, location, and spacing of 120 mm circular openings affect ultimate load capacity, initial stiffness, ductility, and overall failure response. Seven half-scale composite beams were fabricated and tested, including two reference beams without openings and five beams with different opening arrangements. All specimens had identical geometry, material properties, reinforcement details, shear connector layout, support conditions, and loading configuration; therefore, the effect of opening arrangement could be isolated. The findings showed that the central opening located in the pure bending region caused a 14.5% reduction in ultimate load and a 31.7% reduction in stiffness compared with the reference beam. The specimen with two openings in the shear span showed a response close to the reference beam, while the specimen with ten distributed openings exhibited the largest reductions, with 23.4% loss in ultimate load and 23.7% loss in stiffness. The novelty of this work lies in providing a controlled experimental comparison of large 120 mm circular web openings in steel–concrete composite beams and linking their structural performance to opening location, distribution, and serviceability response.