Catalysts comprising palladium and biaryl monophosphine ligands provide highly active systems for the borylation of aryl and heteroaryl chlorides. Symmetrical and unsymmetrical biaryl products can also be prepared directly from two aryl chlorides without isolation of the intermediate boronate esters. Computational studies provide insight into the roles of the biaryl phosphine ligand and the KOAc base in the catalytic cycle.