Allston was the son of Robert Allston, Governor of South Carolina and Adele Petigru. He married Ellen Stanley Robinson, by whom he had three children.
He graduated from the USMA, West Point, NY (where he probably met JW) in 1853. He became Colonel in the 4th Alabama Infantry, C.S.A, and worked for his father's office from 1857 to 1858. He cultivated the family rice plantation in South Carolina from 1857 to 1861. In 1877 he became clergyman for the Protestant Episcopal Church.
George W. Cullum, Register of Graduates and Former Cadets of the United States Military Academy, New York, 1980 edition, p. 245.