Carnan was born in Reading, son of the printer William Carnan. However, when his father died shortly after his birth, his mother married the journeyman John Newbery and the family moved to London in 1744. Carnan worked in his stepfather’s business with Newbery’s nephew, Francis. He was refused the freedom of the Stationers’ Company in 1755. Following Newbery’s death, Carnan and Francis entered a publishing partnership. They specialised in publishing hugely popular diaries, calendars, and pocket-books, which, in their contents, were remarkably similar to that of an almanac. The Stationers’ Company, feeling their monopoly over almanacs threatened, issued an injunction against Carnan to cease selling these works. Carnan answered them in court and in 1775, the case was found in his favour. However, he was not so successful in challenging the monopoly of the King’s Printers nor in preventing increased stamp duty on sheet almanacs. When Carnan died in 1788 and no doubt against the deceased’s wishes, the executors of his state sold his almanac interests to the Stationers’ Company.