Very little is known about Toland's true origins other than the fact that he was born in Ardagh on the Inishowen Peninsula, a predominantly Catholic and Irish speaking region, in north west Ulster. It is likely that he was originally christened "Seán Eoghain Ui Thuathalláin", thus giving rise to the sobriquet "Janus Junius Toland". After having converted to Protestantism around the age of 16, he obtained a scholarship to study theology at the University of Glasgow.

He would also later attend university at Edinburgh and at Leiden in Holland. His first book Christianity Not Mysterious (1696) was burnt by the public hangman in Dublin. He escaped prosecution by fleeing to England, where he spent most of the rest of his life.

He was the first person called a freethinker (by Bishop Berkeley) and went on to write over a hundred books in various domains but mostly dedicated to criticizing ecclesiastical institutions. A great deal of his intellectual activity was dedicated to writing political tracts in support of the Whig cause. Many scholars know him for his role as either the biographer or editor of notable republicans from the mid-17th century such as James Harrington, Algernon Sidney and John Milton. His works "Anglia Libera" and "State Anatomy" are prosaic expressions of an English republicanism which reconciles itself with constitutional monarchy.

Toland is generally classed with the deists, but at the time when he wrote Christianity not Mysterious he was careful to distinguish himself from both skeptical atheists and orthodox theologians. After having formulated a stricter version of Locke's epistemological rationalism, Toland then goes on to show that there are no facts or doctrines from the Bible which are not perfectly plain, intelligible and reasonable, being neither contrary to reason nor incomprehensible to it. All revelation is human revelation; that which is not rendered understandable is to be rejected as jibberish.

After his Christianity not Mysterious, Toland's "Letters to Serena" constitute his major contribution to philosophy. In the first three letters, he develops an historical account of the rise of superstition arguing that human reason cannot fully ever liberate itself from prejudices. In the last two letters, he founds a metaphysical materialism grounded in a critique of monist substantialism. Later on, we find Toland continuing his critique of church government in Nazarenus which was first more fully developed in his "Primitive Constitution of the Christian Church", a clandestine writing in circulation by 1705.

The first book of "Nazarenus" calls attention to the right of the Ebionites to a place in the early church. The thrust of his argument was to push to the very limits the applicability of canonical scripture to establish institutionalized religion. Later works of special importance include Tetradymus wherein can be found Clidophorus, a historical study of the distinction between esoteric and exoteric philosophies.

Toland influenced Baron d'Holbach's ideas about physical motion. In his Letters to Serena, Toland claimed that rest, or absence of motion, is not merely relative. Actually, for Toland, rest is a special case of motion. When there is a conflict of forces, the body that is apparently at rest is influenced by as much activity and passivity as it would be if it were moving.

His Pantheisticon, sive formula celebrandae sodalitatis socraticae (Pantheisticon, or the Form of Celebrating the Socratic Society), of which he printed a few copies for private circulation only, gave great offence as a sort of liturgic service made up of passages from heathen authors, in imitation of the Church of England liturgy. The title also was in those days alarming, and still more so the mystery which the author threw around the question how far such societies of pantheists actually existed.

The term "pantheism" was coined by Toland to describe the philosophy of Spinoza. Toland was involved in at least one such society of pantheists: in 1717 he founded the Ancient Druid Order, an organization that continued uninterrupted until splitting into two groups in 1964. Both those groups, The Druid Order and the Order of Bards, Ovates and Druids, still exist today.

See also Mosheim's Vindiciae antiquae christianorum disciplinae (1722), containing the most exhaustive account of Toland's life and writings; A Life of Toland (1722), by one of his most intimate friends; Memoirs of the Life and Writings of Mr John Toland, by Pierre Des Maizeaux, prefixed to The Miscellaneous Works of Mr John Toland (London, 1747); John Leland's View of the Principal Deistical Writers (last ed. 1837); G. V. Lechlers Aeschichte des englischen Deismus (1841); Isaac Disraeli's Calamities of Authors (new ed., 1881); article on "The English Freethinkers" in Theological Review, No. 5 (November, 1864); J. Hunt, in Contemporary Review, No. 6.

Quotations

[Be] cheerful, sober, temperate and free from Superstition.

[Hypatia was] a most beautiful, most virtuous, most learned, and every way accomplish'd Lady; who was torn to pieces by the Clergy of Alexandria, to gratify the pride, emulation, and cruelty of their Archbishop Cyril, commonly but undeservedly styled Saint Cyril.

People ought to be very tender and reserv'd in accusing a Man of any Thing that manifestly turns to his Disadvantage: but making one pass for a Traitor, a Parricide, or Murderer, are nothing, even in the Eys of the World, to charging him with Atheism: for such a Person is not only justly lookt upon as one that has no Reason or Reflection, but likewise as under no Tyes of Conscience, of Obligations or Oaths, when he has an Opportunity of doing Mischief; and so not to be trusted in any private or public Capacity....I could produce many Instances to this purpose from the antient Philosophers; the Heathen Priests represented the primitive Christians as Atheists both in Doctrine and Practice, and the People at their Instigation treated 'em as such; the first Reformers, with their followers, met with the same unjust Measures from the Papists; and, at this present Time, when the Inquisitors can make no other accusation good against their Prisoner, they take Care to Charge him with Atheistical Notions and the most enormous crimes, whereby he's straight condemn'd by the public Voice, and all Men's Ears are stops against any Thing that can be said for one they conceive to be such a wicked Wretch....