Abstract: A kinematical model is proposed for steel-concrete composite beams with slip in the steel beam-concrete slab interface, shear lag in the concrete slab and shear deformation in the steel beam. A warping shape function accounting for the non-uniform transverse distribution of longitudinal displacements in the concrete slab and transverse shear deformation of the beam web are introduced into Newmark's model. A closed-form solution for the case of uniform loading is derived. The model and the solution are then validated by means of four examples, showing the necessity of accounting for the shear deformation of composite beams. In addition, it is found that significant errors result from employing Timoshenko beam elements for the steel beam with shear deformation in 3D finite element modeling of a composite beam.