When he came of age, he found himself in possession of a considerable fortune, and about the same time rejected the Catholic doctrine in favour of the Anglican communion. He began to produce _Satires_, which were not printed, but eagerly passed from hand to hand; the first three are known to belong to 1593, the fourth to 1594, while the other three are probably some years later. In 1596 Donne engaged himself for foreign service under the earl of Essex, and "waited upon his lordship" on board the "Repulse," in the magnificent victory of the 11th of June. We possess several poems written by Donne during this expedition, and during the Islands Voyage of 1597, in which he accompanied Essex to the Azores. According to Walton, Donne spent some time in Italy and Spain, and intended to proceed to Palestine, "but at his being in the farthest parts of Italy, the disappointment of company, or of a safe convoy, or the uncertainty of returns of money into those remote parts, denied him that happiness." There is some reason to suppose that he was on the continent at intervals between 1595 and the winter of 1597. His lyrical poetry was mainly the product of his exile, if we are to believe Ben Jonson, who told Drummond of Hawthornden that Donne "wrote all his best pieces ere he was 25 years old." At his return to England he became private secretary in London to Sir Thomas Egerton, the lord keeper (afterwards Lord Brackley), in whose family he remained four years. In 1600 he found himself in love with his master's niece, Anne More, whom he married secretly in December 1601. As soon as this act was discovered, Donne was dismissed, and then thrown into the Fleet prison (February 1602), from which he was soon released. His circumstances, however, were now very much straitened. His own fortune had all been spent and "troubles did still multiply upon him." Mrs Donne's cousin, Sir Francis Wooley, offered the young couple an asylum at his country house of Pyrford, where they resided until the end of 1604.
During the latter part of his residence in Sir Thomas Egerton's house, Donne had composed the longest of his existing poems, _The Progress of the Soul_, not published until 1633. In the spring of 1605 we find the Donnes living at Camberwell, and a little later in a small house at Mitcham. He had by this time "acquired such a perfection" in civil and common law that he was able to take up professional work, and he now acted as a helper to Thomas Morton in his controversies with the Catholics. Donne is believed to have had a considerable share in writing the pamphlets against the papists which Morton issued between 1604 and 1607. In the latter year, Morton offered the poet certain preferment in the Church, if he would only consent to take holy orders. Donne, however, although he was at this time become deeply serious on religious matters, did not think himself fitted for the clerical life. In 1607 he started a correspondence with Mrs Magdalen Herbert of Montgomery Castle, the mother of George Herbert. Some of these pious epistles were printed by Izaak Walton. These exercises were not of a nature to add to his income, which was extremely small. His uncomfortable little house he speaks of as his "hospital" and his "prison;" his wife's health was broken and he was bowed down by the number of his children, who often lacked even clothes and food. In the autumn of 1608, however, his father-in-law, Sir George More, became reconciled with them, and agreed to make them a generous allowance. Donne soon after formed part of the brilliant assemblage which Lucy, countess of Bradford, gathered around her at Twickenham; we possess several of the verse epistles he addressed to this lady. In 1609 Donne was engaged in composing his great controversial prose treatise, the _Pseudo-Martyr_, printed in 1610; this was an attempt to convince Roman Catholics in England that they might, without any inconsistency, take the oath of allegiance to James I. In 1611 Donne wrote a curious and bitter prose squib against the Jesuits, entitled _Ignatius his Conclave_. To the same period, but possibly somewhat earlier, belongs the apology for the principle of suicide, which was not published until 1644, long after Donne's death. This work, the _Biathanatos_, is an attempt to show that "the scandalous disease of headlong dying," to which Donne himself in his unhappy moods had "often such a sickly inclination," was not necessarily and essentially sinful.