Harris began his publishing career by issuing a religious book, War with the Devil, from his shop in Bell Alley in Coleman Street, London, in 1673. Business prospered and during the next six years he published numerous religious books, including attacks against the Catholics and Quakers. Himself an Anabaptist, he became associated with Shaftesbury and the Whigs and in 1679 joined Titus Oates in exposing the Popish Plot.
On July 7 of that year he published the first number of Domestick Intelligence: or News both from City and Country, later The Protestant (Domestick) Intelligence, and continued its publication, with several interruptions, until April 15, 1681, when it was finally suppressed. Harris was both its publisher and editor.
As Shaftesbury's campaign progressed Harris became more audacious and in the latter part of 1679 published the Appeal from the Country to the City, a seditious pamphlet written anonymously by Charles Blount. The following February Harris was tried, found guilty, and sentenced by Chief Justice Scroggs to stand in the pillory and pay a fine of £500, in default of which he was sent to King's Bench Prison. The House of Commons, under Whig influence, petitioned the King for his release, without effect, but in December he was illegally discharged.
He celebrated his release by publishing his Triumphs of Justice over Unjust Judges, dedicating it to Scroggs, and resumed his propaganda against the papists. He opened a coffeehouse near the Royal Exchange in Cornhill where he sold books, playing cards illustrating all the popish plots, and patent medicines.
With the failure of Monmouth's Rebellion and the accession of James II, he acted with his old audacity and published English Liberties, of which five thousand copies were seized by the authorities. With that he agreed with his Whig friend John Dunton, then in Boston, that Old England was an "uneasy place for honest men, " and he determined to seek refuge in New England. He arrived in Boston, with his son Vavasour and a stock of books, in the fall of 1686 and opened a shop on the south corner of State and Washington streets.
He was surrounded by seven booksellers, but the success of his first publication, John Tulley's Almanach for 1687, established his position, and on July 12, 1687, he returned to London to see his wife and to secure more books. Returning January 25, 1688, he found that the business had further prospered under Vavasour and that the second issue of Tulley's Almanach had been published. Meanwhile, in 1687, his estate had been appraised for taxation purposes and was estimated at £16, as great as the estate of any Boston bookseller.
In November 1688 he again sailed for London, with Judge Sewall as a fellow passenger. He soon returned and published a profitable edition of the new charter. His shop became known as the London Coffee House and in August 1690 he secured a license to sell "Coffee, Tee and Chucaletto. " It became a social center, where women could come, though inns were denied them, and among its patrons were the Mathers, who published some of their books with Harris. On Thursday, September 25, 1690, Harris published Publick Occurrences Both Forreign and Domestick, the first newspaper printed in America. It contained three pages of news, with no advertisements, and was remarkable because the news was chiefly American.
Harris had a marked sense of news value and a vigorous style in writing. He had planned to publish the paper monthly, "or if any Glut of Occurrences happen, oftener, " but the first issue was promptly suppressed by the governor and the council. According to Sewall, it gave "much distaste because not licensed; and because of the passage referring to the French King and the Maquas (Mohawk Indians). " Four days after the paper's appearance a broadside proclaimed the "high resentment and Disallowance" of the authorities and forbade any printing without license. Sometime before 1690 Harris had published The New England Primer, one of the most popular and influential books ever printed in America. He had brought out in London in 1679 The Protestant Tutor, a book designed to teach children spelling, the true Protestant religion, and the iniquities and dangers of the papists. Several similar books had been unsuccessfully published in Boston, perhaps in imitation of the Tutor, but Harris saw the necessity of a radical change, and though he borrowed parts of his Tutor, the New England Primer was a schoolbook for children and not a savage political tract. During 1690 Harris published at least ten books.
The following year he formed a partnership with John Allen, and in 1692 he became the official printer to the governor, a position of influence, though one of difficulty and little profit. In 1693 Green superseded him as official printer and in 1694 he moved from his shop "over-against the old-Meeting-House" to new quarters "at the Sign of the Bible, over-against the Blew Anchor. "
Having determined to return to London, he went early in 1695, leaving Vavasour, assisted by Allen, to close up his business. His last publication was Tulley's Almanach for 1695. In London he turned again to journalism and in May 1695 published the first number of Intelligence Domestick and Foreign. This was followed within three months by three newspapers which failed, but on June 6, 1699, he brought out The London Slip of News, both Foreign and Domestick, which, with its second issue, became the London Post and survived exactly six years. He sold it from his shop at the "Golden Boar's Head, against the Cross Keys in Gracechurch Street, " along with sermons, books, almanacs, and patent medicines.
His frequent quarrels with Doctor John Partridge, whose almanacs he plagiarized, probably attracted the attention of Jonathan Swift and brought about the famous Bickerstaff papers. In the Post he fought bitterly with his old friend Dunton, who replied in his Living Elegy: or, Dunton's Letter (being a word of Comfort) to his Few Creditors (1706). It is to these quarrels that we owe most of our later knowledge of Harris. The London Post ceased publication in 1706 and his last edition of The Protestant Tutor was printed in 1716.
Harris was an ardent Anabaptist throughout his life.
Harris supported the Whig Party.
It is known that Harris was married and had two sons.