Born a slave in Philadelphia, Allen went on to become one of the country´s leading religious figures of the 18th and 19th century. He was known as a dynamic Methodist minister who converted many people, including his owner. The owner allowed Allen to purchase his freedom, which he did.
He returned to Philadelphia and drew so many African Americans into St. George´s Methodist Episcopal Church that difficulties arose between White and Black members of the congregation. In 1787 Blacks were relegated to the gallery at St. George. In response, Allen founded one of the earliest self-help organizations for Blacks, the Free African Society. Along with Absalom Jones, he led a movement of Blacks away from St. George´s to form two separate churches - St. Thomas´s Free African Church within the Protestant Episcopal denomination led by Jones, and the Bethel African Methodist Episcopal Church (Mother Bethel) led by Allen. Allen was later ordained a Bishop.
Allen was one of the first people in the nation to denounce slavery. He also voiced strong disapproval of schemes to send Blacks back to Africa ("colonization.")