AbstractLPt^IVF(Aryl) complexes bearing a bulky bidentate 2‐[bis(adamant‐1‐yl)phosphino]phenoxide ligand (L) demonstrate excellent reactivity and selectivity in the arylation of X−H (X=S, N) bonds of amino acid residues in unprotected peptides under mild, including aqueous, conditions. Stepwise addition of these complexes allowed a convenient one‐pot introduction of different aromatic groups in the X−H bonds of Cys and N terminus. Pt^IV reagents can also be used to further arylate N−H bonds in Lys and Trp providing access to peptides bearing multiple aromatic groups.