John Grattan (1800, Dublin −1871) was an Irish naturalist and anthropologist.

John Grattan was an apothecary in Belfast. He had wide interests in natural history and was a member of the Belfast Natural History Society but is best known for his work on ancient Irish skulls collected by his friend Edmund Getty. He devised a system of skull measurements using an ingenious craniometer. "Grattan's work was almost contemporaneous with that of Anders Retzius, and nearly all of it was done before the German and French Schools had elaborated their schemes of skull measurements^[1]