Composite elements are generally used for special types of structures owing to their high efficiency. This research presents an experimental and theoretical investigation on the flexural behavior of low steel reinforcement ratio steel plate-reinforced concrete composite beams. The experimental program consists of 14 reinforced concrete specimens. Meanwhile, the theoretical study involves the verification of the experimental work and a parametric study on the behavior of the steel plate-reinforced concrete composite beams using nonlinear finite element software (ANSYS 18.1). The theoretical and experimental variables include the shape and thickness of the steel plates, the concrete compressive strength, the number of shear connectors, and the use of epoxy resin. The experimental test results revealed that the use of mild steel plates as a replacement for high-tensile steel reinforcements inversely affects the load-bearing capacity of the steel plate-reinforced concrete composite beams. However, when high-tensile steel plates were used as additional reinforcements, the nonlinear finite element analysis predicted up to a 40% increase in the values of the ultimate loads for the composite beams.