Sheridan, Thomas (1646–1712), writer, royal official, and Jacobite, was born in St John's, near Trim, Co. Meath, fourth son of Denis Sheridan (qv), a Church of Ireland clergyman from Co. Cavan, and an Englishwoman named Foster. In the rebellion of 1641 Denis and his family had to flee Cavan, and it was in this period of exile that Thomas was born. Brought up a protestant, Thomas entered TCD in January 1661, graduating with a BA (1664), and was elected to a fellowship (1667). He entered the Middle Temple in June 1670, but soon abandoned the law to become collector of the customs in Cork. His next few years were spent in a series of speculative financial projects involving various Irish revenues, which seem to have brought him a degree of wealth. In the process he began to acquire powerful patrons, notably the duke of Ormond (qv) and, ultimately, James (qv), duke of York.
By 1677 Sheridan had left Ireland for England. He was clearly a rising presence, for in 1677, as part of Ormond's entourage, he received an honorary DCL from Oxford University (where Ormond was chancellor) and in 1679 was elected a fellow of the Royal Society. In 1678 he published, anonymously, A discourse of the rise & power of parliaments. In this text Sheridan, like Locke, advocated religious toleration (publishing before Locke's celebrated Letter concerning toleration), but, unlike the whig writer, included Roman catholicism among the creeds to be tolerated. He further argued that intolerance in Ireland made that kingdom vulnerable to French subornation, thereby undermining the acknowledged legitimacy of the Stuart dynasty in that country. By the summer of 1678 the ‘popish plot’, with its virulent anti-catholicism, made a defence of toleration a risky affair, and Sheridan quickly issued a second edition of his book with a preface that denied that he had any sympathy for subversive political movements. He was, however, to fall victim to the hysteria surrounding the ‘popish plot’ and exclusion crisis. By now in the duke of York's circle, he followed the duke into exile in Flanders in the wake of the exclusion crisis, and returned on the same ship as James. This relationship made him vulnerable to attack, and in December 1680 he was imprisoned on suspicion of complicity in the ‘popish plot’, and had to defend himself before the English house of commons, eventually gaining release in early 1681. He clearly retained royal favour, for Charles II asked him to produce proposals for farming the Irish revenue, and in 1682 awarded him a lump sum of £1,000 and an annual pension of £500.
In 1683 or 1684 he married Helen (c.1662–1702), daughter of Thomas Appleby of Lynton-on-Ouse, Yorkshire, a Roman catholic. They had four children – two sons and two daughters – all brought up as Roman catholics. James, duke of York, became king in 1685, and Sheridan announced his conversion to Roman catholicism in 1686, a matter of days after a decision of the courts effectively allowed catholics to hold public office. In late 1686 Sheridan was, against his wishes, made secretary to Lord Tyrconnell (qv), the newly appointed lord deputy of Ireland, and, more to his liking, was subsequently appointed first commissioner of the Irish revenue. Sheridan was horrified by the opinions and policies of Tyrconnell, whom he characterised as a bigoted catholic, who wished to promote the interests of his fellow Old English, and who sought ultimately to break Ireland's link with Britain. Sheridan, according to a memoir he wrote in 1702 (An historical account) saw his own role as that of promoting what he took to be James's policy of religious and ethnic even-handedness. The relationship between the two men rapidly deteriorated, and Tyrconnell used his power and influence to have Sheridan found guilty of corruption and stripped of all his offices in January 1688.
Sheridan followed James II into French exile in January 1689. His initial contribution to the Jacobite cause was to produce a literary imposture, A letter from a nobleman in London . . . , which was fabricated in the style of the arch-trimmer Lord Halifax, and which imputes duplicity to William of Orange (qv) and stupidity to his English backers. The success of this pamphlet seems to have encouraged James to ask Sheridan to write a formal defence of his reign. A draft of ‘The king of Great Britain's case’ was produced in 1692, and – although amended by James – remained unpublished, initially due to policy/strategy differences among the Jacobite court, and finally, if Sheridan is to be believed, to James's ultimate belief that he was not going to be restored.
Sheridan also produced a defence of the Irish catholic clergy, following their banishment from Ireland in 1697. He went on a diplomatic mission to the Palatinate in 1695 and was made a commissioner of the Stuart royal household in 1699. In 1709 Sheridan finished a manuscript entitled ‘Political reflexions on the history and government of England’, which was also to remain unpublished. This text vehemently expresses the changes that had been gradually going on in Sheridan's thinking since his period of exile. The tone is intolerant and anti-democratic – an uncompromising royal absolutism is defended, as is a policy of religious intolerance against protestantism. The catholic Irish are extolled as the Stuarts’ most loyal subjects, whose fidelity (most unjustly) has brought them nothing but death, dispossession, and exile, while protestant Ireland, though thoroughly disloyal, has prospered.
Sheridan died 17 March 1712 (NS) at Saint-Germain-en-Laye and was buried there. His eldest son, Thomas (qv) (1684–1746), became under-governor to Prince Charles Edward Stuart and was one of the ‘seven men of Moidart’ who landed on the Scottish coast with the prince in July 1745, and who took part in the battle of Culloden in the following year. He was granted a (Jacobite) Irish baronetcy in 1726. Sheridan's eldest brother, William (qv), Church of Ireland bishop of Kilmore and Ardagh, was the only Irish bishop who refused to swear the oath of allegiance to William and Mary, and was, as a consequence, stripped of his office. The unpublished manuscripts of Sheridan are to be found in the Stuart papers in the royal archives at Windsor Castle.