Metallo-supramolecular polymers, which were synthesized via the 1 : 1 complexation of metal ions with ditopic organic ligands, showed unique electro- and photo-chemical properties based on the metal–ligand or metal–metal interactions. Fe(II)-, Ru(II)- and Cu(II)-based metallo-supramolecular polymer films exhibited reversible electrochromic behaviour and electrochromic display devices were successfully fabricated. A polymer containing both Fe(II) and Ru(II) ions exhibited multi-colour electrochromic properties. Ionic conductivity of a Ni(II)-based polymer film was significantly enhanced with increasing humidity, and real-time humidity sensing was realized by utilizing the polymer film. A Eu(III)-based polymer showed vapoluminescence. Reversible switching of emission was achieved in the polymer with Fe(II) and Eu(III) ions introduced in an alternating manner.