He was an assistant surgeon under Louis Isidore Duperrey on La Coquille during its circumnavigation of the globe (1822–1825).
Along with René Primevère Lesson he collected numerous natural history specimens in South America and the Pacific.
Garnot had a severe attack of dysentery and was sent back with some of the collection on the Castle Forbes.
With Lesson he wrote the zoological section of the voyage's report, Voyage autour du monde exécuté par order du roi sur la corvette La Coquille (1828–1832).
The widely distributed parthenogenetic Indo-Pacific house gecko Hemidactylus garnotii A.M.C.