Henry Dwight Sedgwick III (September 24, 1861 – January 5, 1957) was an American lawyer and author.

He had an older sister, Jane Minot (1859-1918), and three younger brothers, Theodore (1863–1951), Alexander "Aleck" (1867–1929) and Ellery Sedgwick.

[2] Sedgwick graduated from Harvard University in 1882, and studied law in Boston until 1884 when he was admitted to the bar.

He also was a member of the American Academy of Arts and Sciences (Boston) and the Massachusetts Historical Society.

He later became an author and wrote several historical biographies on Isaac Thomas Hecker, Henry of Navarre, Alfred de Musset, and Marcus Aurelius.

Their eldest son Henry IV (known as Halla) died of pneumonia at the age of 17.

[5] Robert Minturn Sedgwick was a Harvard Crimson football athlete, as was his father, who started at left tackle for two teams—1919 and 1920—that defeated Yale, the 1919 team named national champions.