Numerical solutions have been obtained for a diffusion flame in the two-dimensional, laminar, steady, viscous, multicomponent, compressible mixing layer in the presence of a pressure gradient by using the boundary layer approximations and solving the x−momentum, energy, and species conservation equations. The numerical solutions have been validated against similarity solutions, and then are extended to cases where no similarity solution exists. The numerical solutions are used to study the ignition process and the flame structure in an accelerating transonic mixing layer. It is shown how ignition length depends upon initial temperature, initial pressure, initial velocity, transport properties, and pressure gradient. Ignition is found to occur on the high-temperature air side. Oxidation kinetics and transport are both controlling in the upstream ignition region. Further downstream, transport is controlling in the fully established flame. The boundary layer approximation is found to be valid everywhere including the upstream ignition region.