Ultra-high performance concrete (UHPC) reinforced with micro steel fibres combines the excellent properties of both material components. Due to the dense structure of the UHPC, high compressive strengths can be achieved, while the steel fibre reinforcement ensures a pseudoductile post‑cracking behaviour under tensile loading. After initiation of crack formation in the UHPC matrix, the crack‑bridging load‑bearing effect of the micro steel fibres is activated. As the bond limit is exceeded, damage to the bond occurs followed by a controlled failure of the material due to fibre pull-out. To describe the phenomenological processes of crack initiation, fibre activation, and fibre pull-out in ultra-high performance fibre-reinforced concrete (UHPFRC) at the macro level, a material model based on the strain energy density in mixed formulation is developed. The volume contents of the UHPC matrix and the fibres are taken into account in the model equations under consideration of strain equivalence. The elastic material behaviour is extended by a model for the crack formation in the UHPC matrix and the fibre pull-out of the micro steel fibres with the method of Lagrange multipliers. For the numerical analysis with the finite element method (FEM), a mixed‑hybrid formulated element is used. Approaches with generalised free values to describe the stresses, the crack strain and the fibre pull-out length over the element domain are chosen. The stiffness matrix is formed by static condensation of all variables of the element domain. The arc-length method is used to find a converging solution for the unstable material behaviour that occurs when the bond limit between the UHPC matrix and the micro steel fibres is exceeded. Numerical simulations of selected examples show that the material model can describe the damage processes occurring in the composite material under tensile loading homogenised on the macro level. The crack formation of the UHPC matrix and the fibre pull-out of the micro steel fibres are dependent on the strengths, the fibre volume content, the fibre effectiveness and the bond characteristics. Especially the properties of the fibres significantly control the post‑cracking behaviour.