This article presents a numerical simulation of three-dimensional flow and heat transfer in a channel with a backward-facing step. Flow was considered to be steady, incompressible, and laminar. The flow medium was treated as radiatively participating. Governing momentum, energy, and the radiative transfer equations were solved by a finite-volume method. Extensive validation studies were carried out. The SIMPLE algorithm was used to link pressure and velocity fields. The combined convective-radiative heat transfer was studied by varying optical thickness (τH= 0.1, 0.2, and 0.4) and scattering albedo (ω = 0, 0.25, 0.5, 0.75, and 1). Variation of thermophysical properties with temperature was considered in this study. Effects of those radiative parameters on velocity, bulk temperature, and Nusselt number are presented in detail. The study goes further to investigate the variation of reattachment length with radiative parameters. The thermal penetration decreased with a decrease in optical thickness and an increase in scattering albedo. Thermal penetration increased with increasing optical thickness and decreasing scattering albedo. The reattachment length varied with temperature as a result of variation of thermophysical properties with temperature.