Breschet made many contributions in comparative anatomy and research of zoonotic diseases. In 1813 with François Magendie (1783-1855) he demonstrated that rabies can be transmitted from the saliva of humans to dogs. He also discovered the rete mirabile in whales and dolphins, which is a vascular network that allows these mammals to survive and adapt at ocean depths.
He did extensive anatomical studies of veins of the cranium and spine, and made important investigations of the auditory system in vertebrates. He provided a comprehensive description of the utricle and saccule of the inner ear, and is credited for introducing the terms otoconia and helicotrema. The helicotrema is sometimes referred to as "Breschet's hiatus", which is a passageway that connects the scala tympani and scala vestibuli at the top of the cochlea. Breschet has several other anatomical terms named after him, including:
Histoire anatomique et physiologique d'un organe de nature vasculaire découvert dans les Cétacés, Suivie de quelques considérations sur la respiration de ces animaux et des amphibies, 1836
