Benton was born in Neosho, Missouri, United States, on April 15, 1889, into an influential family of politicians. He was the son of Elizabeth Wise Benton and Maecenas Eason Benton, a lawyer and four times a congressman from 1897 until 1905.
His father was known as the "little giant of the Ozarks". Maecenas Benton named his son after his own great-uncle, Thomas Hart Benton, one of the first two United States Senators elected from Missouri. Thomas Benton later recalled that "politics was the core of our family life."
Thomas Benton had two younger sisters, Mary and Mildred, and a younger brother, Nathaniel.