Processes are provided for producing a diesel fuel product having a sulfur content of 10 ppm by weight or less from feed sources that include up to 50% by weight of a biocomponent feedstock. The biocomponent feedstock is co-processed with a heavy oil feed in a severe hydrotreating stage. The product from the severe hydrotreatment stage is fractionated to separate out a diesel boiling range fraction, which is then separately hydrotreated.