He was educated at the public schools of Laramie, Wyoming, where the family had moved in 1913 after his father became Dean of St Matthew's Cathedral.
He studied at the University of Wyoming, and then at Kenyon College from where he graduated in 1933 with a Bachelor of Arts.
He transferred to the Episcopal Theological Seminary, graduating in 1936 with a Bachelor of Divinity.
Thornberry was ordained deacon on June 14, 1936, and priest on April 24, 1937, by Bishop Henry Hobson of Southern Ohio.
[2] He married Virginia Lee Morrissett on November 23, 1940, and eventually had two children.