A stereoselective synthetic route to homo‐ and heteroleptic facial tris‐cyclometalated PtIV complexes is reported, involving the oxidative addition of 2‐(2‐pyridyl)‐ or 2‐(1‐isoquinolinyl)benzenediazonium salts to cis‐[Pt(C^N)2] precursors, with C^N=cyclometalated 2‐(p‐tolyl)pyridine (tpy), 2‐phenylquinoline (pq), 2‐(2‐thienyl)pyridine or 1‐phenylisoquinoline (piq), to produce labile diazenide intermediates that undergo photochemical or thermal elimination of N2. The method allows the preparation of derivatives bearing cyclometalated ligands of low π–π* transition energies. The new complexes exhibit phosphorescence in fluid solution at room temperature arising from triplet ligand‐centered (3LC) excited states, which, in the cases of the heteroleptic derivatives, involve the ligand with the lowest π–π* gap. The heteroleptic piq derivatives exhibit fluorescence and dual phosphorescence from different ligand‐centered excited states in rigid media, demonstrating the potential of cyclometalated PtIV complexes as multi‐emissive materials.