New Mn(II), Ni(II), Co(II) and Cu(II) complexes of an azo dye ligand based on p‐phenylenediamine with 5‐nitro‐8‐hydroxyquinoline were synthesized and characterized using elemental analysis, inductive coupled plasma analysis, molar conductance, powder X‐ray diffraction, thermogravimetric analysis, magnetic moment measurements, and infrared, 1H NMR, electron ionization mass and UV–visible spectral studies. The spectral and analytical data reveal that the azo dye ligand acts as a monobasic bidentate ligand via deprotonated OH and nitrogen atom of the quinoline ring. The data support the formulation of all complexes with a 2:1 ligand‐to‐metal ratio, except the Mn(II) complex that has a mononuclear formula. All complexes have an octahedral structure. The molar conductance data reveal that all the metal complexes are non‐electrolytic in nature. From the X‐ray data, the average particle size of the ligand and its complexes is 0.32–0.64 nm. The colour fastness to light, washing, perspiration, sublimation and rubbing of the prepared ligand and its complexes on polyester fabrics and colorimetric properties were measured. The results reveal that the ligand and its complexes have a good to moderate affinity to polyester fibres. New Mn(II), Ni(II), Co(II) and Cu(II) complexes of an azo dye ligand were synthesized. Spectral and analytical data revealed that the azo dye ligand acts as a monobasic bidentate ligand. X‐ray data for the investigated compounds were obtained. The colour fastness of the prepared ligand and its complexes on polyester fabrics and colorimetric properties were measured.