Fiber-reinforced polymer (FRP)-confined concrete members have been attracting extensive research attention. The mechanical behavior of concrete under uniform FRP confinement, as is found in FRP-confined circular concrete columns under concentric compression, has been well understood and can be accurately predicted using existing theoretical models. However, the same cannot be said about concrete under non-uniform confinement, as is found in FRP-confined concrete members with a non-circular cross-section or subjected to eccentric compression. The major obstacle is the lack of an accurate constitutive model for concrete under non-uniform passive confinement. The existing analytical stress-strain models for FRP-confined concrete are essentially one-dimensional (1D) (i.e. the so-called design-oriented models) or two-dimensional (2D) (i.e. the so-called analysis-oriented models), and are therefore not directly applicable to concrete under non-uniform FRP confinement which requires three-dimensional (3D) stress and strain relationships. The conventional plasticity models, though having the ability to predict 3D stress-strain responses, have been developed to reflect the experimental behavior of concrete under active stresses, and are thus incapable of accurate prediction of the behavior of FRP-confined concrete. An improvement to such a conventional plasticity model is to embed an accurate 2D analysis-oriented analytical model for FRP-confined concrete into a 3D plasticity model, leading to an analytically augmented (AA) plasticity model. However, such a combination involves an inherent approximation in connecting the 2D response of the former with the 3D response of the latter, and as a result such an AA plasticity model is still inaccurate for concrete under substantially non-uniform FRP confinement. This paper first presents a new plasticity constitutive model for concrete developed by the authors, in which a novel potential surface is employed to accurately predict the 3D stress-strain behavior of concrete under non-uniform passive confinement. The model has been implemented with the general-purpose finite element package ABAQUS, and its performance is demonstrated through simulating the mechanical behavior of an FRP-confined elliptical concrete column under concentric compression.