Paul Hallez (10 September 1846 - 2 November 1938) was a French zoologist and embryologist born in Lille.
In 1864 he began his scientific career as a préparateur of natural history under Jules Gosselet (1832–1916) at the Faculté des Sciences in Lille.
He later defended his thesis at the Sorbonne with an award winning treatise on Turbellaria titled Contributions à l'histoire naturelle des turbellariés.
In 1888 he founded a marine biological laboratory at Le Portel that was associated with the Université Lille Nord de France.
His scientific work largely dealt with flatworms, nematodes, the phyla- Bryozoa and Nemertea, etc.