Daniel Darwin Pratt (October 26, 1813 – June 17, 1877) was a United States senator from Indiana.

Born in Palermo, Maine, he moved to New York with his parents, who settled in Fenner.

He moved to Indiana in 1832 and taught school; in 1834, he settled in Indianapolis and was employed in the office of the Secretary of State.

Pratt was appointed by President Ulysses S. Grant as Commissioner of Internal Revenue, holding that office in 1875 and 1876.

Pratt practiced law with his nephew, Daniel P. Baldwin, who later became Indiana Attorney General (1880–1882).