He began his career by robbing his father, and, after a rambling life, took to coining false money, for which offence and others he was many times imprisoned. False to everyone, he first tried to involve James Scott, 1st Duke of Monmouth and others by concocting information about a Presbyterian plot against the throne, and this having been proved a lie, he pretended to have discovered a Catholic plot against Charles II. This was known as the Mealtub Plot, from the place where the incriminating documents were hidden at his suggestion, and found by the king's officers by his information.
Mrs Elizabeth Cellier, in whose house the tub was, almoner to the Countess of Powis, who had befriended Dangerfield when he posed as a Catholic, was, with her patroness, actually tried for high treason and acquitted (1680). For a time Dangerfield was used as a secondary witness in the Popish Plot trials to supplement the evidence of Titus Oates and William Bedloe, but his character was so unsavoury, even compared to the other informers, that Chief Justice William Scroggs finally told juries to disregard the evidence of "so notorious a villain". Dangerfield, when examined at the bar of the House of Commons, made other charges against prominent Roman Catholics, and attempted to defend his character by publishing, among other pamphlets, Dangerfield's Narrative.
This led to his trial for libel, and on 20 June 1685 he received sentence to stand in the pillory on two consecutive days, be whipped from Aldgate to Newgate, and two days later from Newgate to Tyburn. On his way back he was struck in the eye with a cane by a barrister, Robert Francis, and died shortly afterwards from the blow. The barrister was tried and executed for the murder, somewhat to the surprise of the public, the popular view being that the death " could hardly have been even called manslaughter".
He is the subject, and perhaps the author, of Don Tomazo, or The Juvenile Rambles of Thomas Dangerfield (1680), a comic, self-consciously literary novel that presents Dangerfield as a clever and resourceful rogue. It is reprinted in Spiro Peterson's The Counterfeit Lady Unveiled and Other Criminal Fiction of Seventeenth-Century England (1961) and in Paul Salzman's Anthology of Seventeenth-Century Fiction (1991).