The paper reports the observation of a magnonic Dicke superradiant phase transition (SRPT) in ErFeO₃, where the role of the photonic mode (two-level atoms) is played by an Fe³⁺ magnon mode (Er³⁺ spins). The absence of the diamagnetic term in the Fe³⁺–Er³⁺ exchange coupling ensures that the no-go theorem does not apply, allowing for the SRPT. Terahertz and gigahertz magnetospectroscopy experiments revealed the signatures of the SRPT, including a kink and softening of two spin-magnon hybridized modes at the critical point. The magnonic SRPT is demonstrated through the phase transition between the normal (N) and superradiant (SR) phases, with the Fe³⁺ magnon mode playing the role of the single-mode cavity photons in the Dicke model. The experimental results are accurately reproduced by an extended Dicke model incorporating the single-ion anisotropy energy of Er³⁺ spins. This work opens up possibilities for exploring novel quantum vacuum phenomena in the superradiant phase and provides insights into achieving photonic SRPTs through an exchange pathway.The paper reports the observation of a magnonic Dicke superradiant phase transition (SRPT) in ErFeO₃, where the role of the photonic mode (two-level atoms) is played by an Fe³⁺ magnon mode (Er³⁺ spins). The absence of the diamagnetic term in the Fe³⁺–Er³⁺ exchange coupling ensures that the no-go theorem does not apply, allowing for the SRPT. Terahertz and gigahertz magnetospectroscopy experiments revealed the signatures of the SRPT, including a kink and softening of two spin-magnon hybridized modes at the critical point. The magnonic SRPT is demonstrated through the phase transition between the normal (N) and superradiant (SR) phases, with the Fe³⁺ magnon mode playing the role of the single-mode cavity photons in the Dicke model. The experimental results are accurately reproduced by an extended Dicke model incorporating the single-ion anisotropy energy of Er³⁺ spins. This work opens up possibilities for exploring novel quantum vacuum phenomena in the superradiant phase and provides insights into achieving photonic SRPTs through an exchange pathway.