Thomas Seir Cummings (1804–1894) was an English-American miniature painter and writer.

Thomas Seir Cummings was born at Bath, England on August 26, 1804.

He painted miniatures in water color, and many of his sitters were well-known contemporaries of the artist.

In 1826 he helped to found the National Academy of Design, was its treasurer for many years and one of its early vice presidents.

He also wrote an account of its history, entitled Historic Annals of the National Academy from its Foundation to 1865 (Philadelphia, 1865).