Frank Hall Knowlton was born on September 2, 1860, in Brandon, Vermont.

He was an American paleobotanist, ornithologist, and naturalist. He studied natural history at Middlebury College (B.Sc., 1884; M.Sc., 1887). He visited the U.S. National Museum in Washington in 1884, while preparing an exhibit for the World Cotton Centennial in New Orleans and met the paleobotanist Lester F. Ward. He later became his assistant on the Geology Survey and studied fossil wood in the lignites of the Potomac. He joined the U.S. Geological Survey as an assistant paleontologist in 1894 and was promoted to geologist in 1907. He was a professor at George Washington University (1887-1896) and curator of botany and fossil plants at the U.S. National Museum (1887-1889). He joined the Columbian College as a Professor of Botany and received a Ph.D. in 1896 and a D.Sc. in 1921. He founded and edited the journal The Plant World in 1897. Knowlton also authored many articles and books including "Birds of the World" (1909) and "Plants of the Past" (1927).

In 1887, he married Anne Stirling Morehead (1857–1890) and in 1894, he married Rena Genevieve Ruff (1873–1966). He died on November 22, 1926, in Ballston, Arlington, Virginia.