Monodispersed nanoplatelets of Ni-doped ZnO with tailored room-temperature ferromagnetism (RTFM) were synthesized through a facile and highly reproducible process involving a Zn²⁺–Ni²⁺-polymer composite precursor. Single phase ZnO of P63mc hexagonal wurtzite crystal structure lies in the derived samples (Zn_1-xNi_xO, x = 0–0.1) after firing the corresponding precursors at 400–600 °C for 2 h in ambient air. Structural and optical analyses confirmed the incorporation of Ni²⁺ions into the ZnO lattice by replacing the Zn²⁺ ions. Microstructural analysis revealed the uniformity in the shape and size of the finely dispersed particles in the form of hexagonal nanoplatelets. Typical samples derived at 500 °C have an average diameter, D ∼22 nm with <5 nm thickness (δ). The observed RTFM ordering in the derived samples can be precisely tuned by controlling the Ni concentration and the processing temperature. The synthesis technique provides excellent control over the doping concentration and microstructure in these diluted magnetic semiconductor (DMS) materials for pertinent applications in wide areas starting from spintronics and magneto-optics to biosensors.