In this work, MgO supported Fe–Co–Mn nanoparticles (MgO-FCM-NPs) are synthesized and utilized as adsorbent for the successful removal of Rhodamine B dye (RhB) from aqueous environments. In the first step, the synthesized MgO-FCM-NPs are identified using scanning electron microscopy (SEM), vibration sample magnetization (VSM), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) techniques. In the second step, the effects of different adsorption conditions such as solution pH (3–13), dye concentration (10–120 mg L−1), adsorbent dosage (0.04–0.12 g L−1), temperature (298–318 K) and contact time (20–100 min) are investigated. The pH 7 is found to be the optimized pH and the equilibrium is reached in 60 min for RhB adsorption onto MgO-FCM-NPs. The maximum adsorption capacity of RhB onto MgO-FCM-NPs is found to 1106 mg g−1 at pH 7, temperature 318 K and contact time 60 min using 120 mg L−1 RhB concentration. The adsorption data is fitted better to Langmuir isotherm model (R2 = 0.999) in comparison to Freundlich and Temkin equilibrium isotherm models. The n (Freundlich constant) values are in between 1–10, suggesting desirable adsorption of RhB onto MgO-FCM-NPs. Further the adsorption process of RhB onto MgO-FCM-NPs is followed pseudo-second-order kinetics (R2 = 0.9999). The negative values of Gibbs free energy (ΔG°) represents spontaneity of the process and the positive values of enthalpy (ΔH°) of RhB adsorption onto MgO-FCM-NPs indicates the endothermic nature. Finally, it is concluded that the MgO-FCM-NPs could be used for effective RhB removal from textile effluents.