The quick recombination of charge carriers and the low oxidizing ability of VB holes of g-C₃N₄ limits its practical application. Herein, we have synthesized a visible-light sensitive Fe(III)-grafted K-doped g-C₃N₄/rGO heterostructure photocatalyst to tackle the above problem so as to achieve enhanced photocatalytic activity. The prepared samples were characterized by standard analytical techniques such as XRD, FT-IR, EPR, SEM, TEM, DRS and PL spectroscopy. EPR analysis reveals that the grafted iron exists in +3 oxidation state in the composite material. As compared to pristine g-C₃N₄, surface grafted nanocomposite photocatalyst exhibits excellent photocatalytic performance for the degradation of Rhodamine B (RhB), Methylene Blue (MB) and Methyl Orange (MO) under visible light irradiation. The enhanced activity could be attributed to the creation of defect levels in the band gap, shift of absorption band towards the visible region and intimate interfacial interactions between graphene and g-C₃N₄, effectively promoting separation of photoinduced charge carriers. The idea to tune the bandgap of graphitic carbon nitride by introducing alkali metal along with its composite formation with graphene could present a new concept to effectively steer the photocatalytic activity.