Cyclic plasticity and viscoplasticity of an advanced nickel-based superalloy have been described using the Chaboche unified constitutive model. Experiments have been developed to obtain the full cyclic stress–strain and stress relaxation data at 650 °C. A step-by-step method has been used to obtain the initial material parameters, while a non-linear least-square approach has been used to obtain the optimised material parameters. Compared with our early work [Int J Fatigue 25 (2003) 413; Mech Mater 33 (2001) 593], much improved results have been obtained for the simulation of the transient cyclic stress–strain and stress relaxation as well as the steady-state behaviour with no additional terms or parameters introduced. The depiction of creep and combined cyclic stress–strain and stress relaxation curves seems also to be very encouraging.