Low-dimensional antiferromagnetic van der Waals materials have emerged as a versatile platform for exploring exotic spin dynamics and magnetic phases, yet electrically accessing these phenomena remains a major challenge because of their vanishing net magnetization and highly insulating nature. Here, we demonstrate that graphene can act as an ultrasensitive electrical transducer of hidden spin dynamics in two-dimensional antiferromagnets. By integrating graphene with the van der Waals antiferromagnet FePS₃, low-temperature transport measurements combined with magnetic-field and gate-voltage control reveal multiple resistance anomalies well below the Néel temperature. Their distinct temperature, magnetic-field, and carrier-density dependences enable us to associate these anomalies with magnon excitations and with a low-temperature magnetic reconfiguration of the antiferromagnetic state, both of which remain largely inaccessible to conventional magnetometry. Density functional theory calculations further show that competing antiferromagnetic spin configurations in FePS₃ are nearly degenerate in energy while producing markedly different electronic responses in the adjacent graphene layer. The pronounced electrostatic tunability of these signatures demonstrates that graphene directly transduces interfacial magnetic dynamics into an electrical signal. Our work establishes graphene/antiferromagnetic van der Waals heterostructures as a versatile platform for the electrical readout of spin dynamics in two-dimensional magnets.