<p>Bright point-defect emitters in hexagonal boron nitride have potential applications in quantum sensing and other technologies. However, it can be difficult to correctly identify the microscopic nature of observed defects, creating challenges for further development. A class of bright emitters exhibiting optically detected magnetic resonance with no resolvable zero-field splitting has been observed in hexagonal boron nitride across a broad range of wavelengths. However, the microscopic structure of the defects and the physical origin of their optically detected magnetic resonance signal have still not been identified. Here we describe a model that accounts for and provides a physical explanation for all key experimental features of the spin-resolved photodynamics of ensembles and single emitters. The model, inspired by the radical-pair mechanism from spin chemistry, assumes a pair of nearby point defects, one of which is optically active. Using first-principles calculations, we show that simple defect pairs made of common carbon defects provide a plausible realization of our model. As well as addressing open questions about defects in hexagonal boron nitride, our model may also explain similar phenomena observed in other wide-bandgap semiconductors.</p>