Literary folk figure. Though a prominent Richmond businessman of his time, John (who was nicknamed "Scotch") is remembered in history as the often-reluctant foster father to an orphaned Edgar Poe. John gave young Edgar a home and a middle name but little in the way of true affection. Their increasingly bitter relationship provided much drama in Edgar's early years and affected the course of Edgar's life.

John Allan emigrated to the United States, settling in Richmond sometime prior to February 1795. He married Francis Keeling Valentine on 5 February 1803 and became a naturalized citizen on 4 June 1804. Frances was often ill and the marriage produced no children. In late December 1811, the Allans brought the recently orphaned Edgar into their home and became his foster parents (they never formally adopted him). Frances was very happy to have a child in the household. John was less enthusiastic but apparently treated Edgar reasonably well at first, after which Edgar took to calling him "Pa."

During the War of 1812, John served as a Private in Capt. Benjamin Pollard's Company, 74th Regiment of Virginia Militia, which was also attached to the 9th (Sharp's) Virginia Regiment. In 1815, John, Frances, and Edgar moved to England for John to pursue business interests, returning to Richmond in 1820. There, John remained for the rest of his life while forming a successful business partnership with Charles Ellis. In addition, the death of his uncle William Galt in 1825 left Allan with a significant inheritance.

As the precocious Edgar grew into a sensitive, creative young man, he and the bottom-line businessman John began to clash more and more. John provided some financial backing for Edgar's attendance at the University of Virginia and later at the United States Military Academy at West Point, but both sojourns ended in mutual recrimination about the nature and extent of that support and helped lead to an irretrievable rift in their relationship. Frances's early death and John's remarriage to Louisa Patterson further deepened an estrangement that continued until John's death.

John had three children with Louisa and also fathered at least three children out of wedlock: Edward (a/k/a "Edwin") Collier; and, in 1830, twin children with Elizabeth Wills of Richmond. He provided for the twins in his will (but left nothing for Edgar). He is buried near his wives and his children, beside Louisa, in the plot he owned.