The selective N‐arylation of p‐aminophenylalanine in polypeptides with pre‐formed palladium oxidative addition complexes is described. The depressed pKa of the aniline NH2 group enables chemoselective C−N bond formation on peptides containing multiple other aliphatic amino groups at lysines or the N‐terminus via Curtin–Hammett control under mild conditions. Using palladium complexes derived from electron‐poor aryl halides, p‐aminophenylalanine is fully arylated in aqueous buffer in as little as one hour at micromolar concentrations. A complementary protocol using the non‐nucleophilic, organic base 1,5‐diazabicyclo(4.3.0)non‐5‐ene (DBN), expands the substrate scope to tolerate electron‐rich functional groups provides up to 97 % conversion. These procedures enable the chemoselective conjugation of functionally diverse small molecule pharmaceuticals to p‐aminophenylalanine containing derivatives of cell‐penetrating peptides.