Born into an influential family, Allen initially favored the colonial cause in the American Revolution, and represented Pennsylvania in the Second Continental Congress from 1775 to 1776.

Andrew graduated from the College of Philadelphia (later named the University of Pennsylvania) in 1759, read law under Benjamin Chew, and then went to London to complete a legal education at the Inner Temple.

When tensions increased before the American Revolution, Allen was one of those critical of the Intolerable Acts passed by the British Parliament in 1774.

He signed the non-importation agreement boycotting British goods in protest of the Boston Port Act, and helped form an independent militia unit, the First Troop Philadelphia City Cavalry, on November 2, 1774.

The instructions given to Pennsylvania's delegates prohibited them from supporting any measures that would lead to independence from Great Britain.

The situation in Philadelphia had become tense as a British army under General Howe drove George Washington's forces out of New York and towards Pennsylvania.

In his diary, James Allen, brother of Andrew, described the precarious situation of those Philadelphians who were suspected of being unsympathetic to the Revolution, and how the Allen family reacted: Houses were broken open, people imprisoned without any color of authority by private persons, and, as was said, a list of 200 disaffected persons made out, who were to be seized, imprisoned, and sent off to North Carolina; in which list, it was said, our whole family was put down.