When he was ten years old, he went to work as an apprentice to his uncle, William Dunlap, a printer and bookseller in Philadelphia.

John eventually bought the business, and at first made a living by printing sermons and probably broadsides and handbills too.

In November 1771, Dunlap, with David C. Claypool began the publication of the Pennsylvania Packet, or General Advertiser, a weekly newspaper.

[1][2][3] During the American Revolutionary War, Dunlap became an officer in the First Troop Philadelphia City Cavalry, and saw action with George Washington at the battles of Trenton and Princeton.

He continued in the First City Troop after the war, rising to the rank of major, and leading Pennsylvania's cavalry militia to help suppress the Whiskey Rebellion in 1794.

Within the same year that Dunlap began printing his daily, he was elected a member of the American Philosophical Society.