Polyelectrolytes carrying multiple negative charges were found to induce the aggregation and self‐assembly of the positively charged platinum(II)–terpyridyl complexes in aqueous media. The aggregation and self‐assembly of the complexes were driven by electrostatic interactions between the polymer and the complex, and by terpyridine ligand π–π stacking and platinum–platinum (metal–metal) interactions. As a result, remarkable UV/Vis and emission spectral changes were observed. The spectroscopic property changes were related to the structural properties of the metal complexes as well as the polyelectrolytes. The induced self‐assembly of the platinum complexes was also strongly affected by the solution properties of the aqueous media, for example, the solution pH, ionic strength, and the percentage of organic solvent added.