Ultralight Majorons are well-motivated dark-matter candidates that can couple to electron spins, generating an oscillating pseudo-magnetic field. We propose a hybrid magnon-qubit haloscope that exploits this interaction to search for Majoron dark matter. In our scheme, the Majoron field resonantly drives the Kittel mode of a ferrimagnetic yttrium iron garnet (YIG) sphere, producing a collective magnon response enhanced by the large spin ensemble. The resulting magnon population is transduced to a superconducting transmon qubit through a cavity-mediated dispersive interaction and detected using quantum-nondemolition Ramsey interferometry. Using experimentally demonstrated parameters for magnon-cavity-qubit systems, we derive the Majoron-induced signal, evaluate the projected sensitivity, and analyze the corresponding mass-scan strategy enabled by magnetic-field tuning, benchmarking the projected reach against existing laboratory and astrophysical constraints on the axion/Majoron-electron coupling. Our results establish hybrid magnon-qubit architectures as a promising quantum-sensing platform for searches for Majoron dark matter and, more generally, ultralight bosonic fields coupled to electronic spins.