He was born in Kansas City, Missouri in 1915 to John Hamilton Thacher and Edith Gilman Thacher. He had an older brother, John Jr., and an older sister, writer Edith Thacher Hurd.[1] Thacher attended the Lawrenceville School in New Jersey and graduated from Princeton University with a degree in economics.[2] Upon graduation from Princeton, Thacher worked for Bankers Trust[3] and simultaneously worked on a law degree from Fordham University.[1] He entered officer training school and served aboard the USS Pensacola during World War II.