Diluted magnetic semiconductors (DMS) find applications in spintronic devices due to their excellent magnetic and magneto-transport properties. Designing room temperature DMS, using non-magnetic transition metal oxides and non-magnetic impurities (i.e., having s, p electrons), is a major challenge for researchers. Using stateof- the-art density functional theory (DFT) simulations, we have predicted for the first time, room temperature ferromagnetism (FM) in C – doped MoO₃ (O substitution defect). Single C impurity in non-magnetic MoO₃, which corresponds to an impurity concentration of 1.04 at.%, induces a magnetic moment of 2.0 μ_B per impurity with FM coupling large enough to sustain room temperature FM. DFT predictions using the generalized gradient approximation (GGA) exchange correlation functional were verified by a hybrid functional, viz., the Heyd- Scuseria-Ernzerhof (HSE06) functional. The system is stable at room temperature and the computed Curie temperature (T_C) is ~565 K. From the relative formation energy it can be inferred that O substituted defect dominates over the interstitial defect; and, C doped MoO₃ can indeed be synthesized with O substituted defect in experiments. The induced FM in this hole doped system is mainly contributed by C and O 2p orbitals and we have established that the Stoner criterion is satisfied to switch on FM by introducing spin polarized defect band at the top of the valence band. Stability of the system, practical feasibility to synthesize C doped MoO₃ and persistence of FM at room temperature signify that C doped MoO₃ can be tailored as room temperature ferromagnets for spintronic applications.