Barclay was a cosmopolitan man of letters who traveled freely between Paris and London. He remained in London from about 1606 until 1616 as a minor court official, then settled permanently in Rome.

Barclay's Euphormionis Lusinini Satyricon (1603–07)—a severe satire on the Jesuits, the medical profession, and contemporary scholarship, education, and literature—is modeled on the style of the Roman satirist Gaius Petronius Arbiter; it is an urbane and facile mixture of prose and verse. Filled with villains and rogues, it contributed to the later development of the picaresque novel. Barclay's most celebrated work was the Argenis, an outstanding example of modern Latin verse. Its political implications were so marked that many editions were supplied with a key to the characters and names. Its fame in Europe persisted; it was reprinted more than 50 times during the 17th century, and literary figures such as William Cowper, Samuel Taylor Coleridge, Richard Crashaw, and Jean-Jacques Rousseau were familiar with the text.