Thomas Mayo Brewer (November 21, 1814 – January 24, 1880) was an American naturalist, specializing in ornithology and oology.

His interest in ornithology was such that he was elected a member of the Boston Society of Natural History in 1835.

He abandoned his career as a doctor after a few years to concentrate on ornithology, writing and politics, later becoming editor of the Boston Atlas in 1840.

However, Brewer is best known as a joint author, with Spencer Fullerton Baird and Robert Ridgway, of A History of North American Birds (3 volumes, 1874), which was the first attempt since John James Audubon's (thirty years prior) to complete the study of American ornithology.

[5] In his last decade of life, Brewer sparred with Elliott Coues over the fate of the House Sparrow, a recently introduced bird that was multiplying far faster than expected.