This paper reports the development of a novel three-dimensional (3D) deterministic model for rough surface line-contact mixed-EHL problems. This model is of great importance because line contacts are found in many mechanical components. The macro aspects of a line-contact problem can be simplified into a two-dimensional (2D) model, but the topography of contacting rough surfaces, micro asperity contacts, and lubricant flows around asperities are often 3D. The present model is based on Hu and Zhu's unified mixed EHL model  and the mixed FFT-based approach formulated by Chen et al . It is numerically verified through comparisons with results from conventional 2D line-contact EHL theories. Numerical examples involving sinusoidal roughness and digitized 3D machined surfaces are analyzed.