Purdie is believed to have been born in Scotland by 1743; however, his exact birth date and exact place of birth are unknown. He was trained at an early age in the skills of printing in his motherland. His immigration to the American British colonies is not known for sure; however, by 1764 he took up residence in colonial Williamsburg, Virginia. At that time he was employed by the then current Williamsburg printer Joseph Royle, as an apprentice.

Purdie succeeded Royle as Editor of the Virginia Gazette on his death in 1766. He formed a partnership with John Dixon until 1774, when Dixon developed a new partnership with william Hunter, the printer at Williamsburg. Purdie then ran a third Virginia Gazette that was similar in articles to the other two Virginia Gazette's being printed in Williamsburg at the time. The newspaper's motto was, "Always for Liberty and the Public Good." Purdie became the official Virginia "public printer" in Williamsburg in 1775, an esteemed lucrative position. He also became the postmaster in Williamsburg by October of that year.

Purdie owned a residence in colonial Williamsburg on a half-acre lot. The legal description of its location is Block 9 Lot 24 and is known further today as building 28A. The house was reconstructed by the Colonial Williamsburg Foundation based on the original underground foundation. It is located on the south side of Duke of Gloucester Street next to the King Arm's Tavern about a block from the Capitol. Purdie purchased the Williamsburg lot and house from the estate of Joanna McKenzie in 1767 with a Dr. James Carter being the administrator. He paid "300 pounds current money of Virginia." The lot already had by 1707 "one good dwelling house thereon." Purdie lived in the house and ran a store that sold yarn goods and wearing apparel from it.

Purdie with his first wife Mary had at least two children. Mary died sometime in or before 1772. It appears that Alexander Purdie, her husband, was selling off her remains of her women's hats Business after her death - at or below cost according to his advertisements of July and August 1772. Purdie married Peachy Devenport in December of that year.

Purdie’s Virginia Gazette was the first American newspaper to publish the complete full text of the United States Declaration of Independence, which was printed on July 26, 1776.

Purdie suffered from dropsy in his later years. He died at Williamsburg in 1779.

Purdie favored the American revolutionary patriots’ cause and his Virginia Gazette newspaper articles reflected that voice. In the time period of the American Revolution, Purdie changed his front page design title several times to reflect his solidarity for the cause of the patriots. At first the masthead read, "Thirteen United Colonies" and "United we stand, divided we fall." Later, an image of a coiled snake was on the masthead with the moto "Don’t tread on me" displaced front and center. It was subtitled "High Heaven to Gracious Ends directs the Storm!"