A native of Ireland, Dunlap arrived in Philadelphia in 1757, apprenticed to his uncle to learn the printing trade. In 1768 Dunlap acquired his uncle's shop, and in 1771 he began publishing a weekly newspaper, The Pennsylvania Packet, or The General Advertiser, which soon became a reliable source of news about the proceedings of the Continental Congress and the progress of the war. By 1784, Dunlap was issuing the Packet as a daily newspaper -- the first in the United States.
Although Dunlap did not become the official printer of the Continental Congress until 1778, it was in Dunlap's shop that the first broadside copies of the Declaration of Independence were printed in July 1776. Continuing to serve the changing needs of the government, Dunlap and his partner David Claypoole printed the Constitution of the United States for use by the Constitutional Convention, and later published it for the first time in the Packet.