Prendergast (Pendergrass), Sir Thomas (1660?–1709), 1st baronet, army officer and Jacobite conspirator, was the eldest of three sons of Thomas Prendergast (d. 1725), a catholic landowner, of Croane, near Newcastle, Co. Tipperary, and his wife, Eleanor, daughter of David Condon. A James Prendergast, also from Tipperary, who was arrested in the Netherlands in 1699 on suspicion of plotting against King William (qv), was a relative. Prendergast was a captain of horse in the Irish army of King James (qv), but was among those who entered William's service after the surrender of Limerick. In 1693 he was listed as one of the officers proposed for the service of Venice against the Turks under the command of Colonel Henry Luttrell (qv), though the project was never carried out.
In early 1696 Prendergast was evidently moving in Jacobite circles in England, where he was trusted enough to be invited to join in what became the best-known of the assassination plots against William. His services were enlisted somewhat late in the plot and he soon decided to warn the government of its existence; he was not the only member of the conspiracy to betray it, but he was the most convincing of the informers, and the one who profited most notably from the episode. His evidence at the trials helped to obtain the conviction of other plotters, eight of whom were executed. The political impact of the plot's revelation was considerable; the position of William and the whigs was enhanced, and both the English and Irish parliaments were prompted to initiate ‘associations’ pledging loyalty to the king.
Prendergast was a catholic at the time of the plot, but his conformity to the established church must have occurred very soon afterwards. Within weeks of revealing the plot he received a pardon and a reward of £2,000 from the king. The Irish government was instructed to find an estate worth £500 a year for him among the forfeited lands. The estate of Roger O'Shaughnessy at Gort, Co. Galway, was identified, though the opposition of Colonel Gustavus Hamilton (qv) – who had a custodiam of it – had first to be overcome. The O'Shaughnessys too resisted, and litigation with Prendergast and his heirs continued for over fifty years. The estate failed to produce the desired income, and various other parcels of land were granted to him. When the English parliament, angered by William's generous grants of Irish forfeited lands to his favourites, passed the Act of Resumption in 1700 Prendergast's standing was high enough for him to be one of the select group of grantees to be excluded by name from its provisions. He was made a baronet in July 1699 and served as MP for Monaghan borough, 1703–9. He served in the army under William and Anne, gaining promotions that culminated in the rank of brigadier-general in February 1709. He was killed on 11 September 1709 at the battle of Malplaquet.
He married, in 1697, Penelope Cadogan, only daughter of Henry Cadogan of Liscartan, Co. Meath, sister of William, 1st Earl Cadogan (qv), and granddaughter, through her mother, Bridget, of the regicide Sir Hardress Waller (qv). They had five daughters and one son, Thomas Prendergast (qv), who succeeded as 2nd baronet on his father's death.
In 1714 a private act of the British parliament was obtained by Penelope Prendergast and William Cadogan (acting as guardian to his nephew), to regularise matters arising from leases of land from the Hollow Sword Blade Company, arranged by Sir Thomas, but not completed at the time of his death. In addition to litigation with the O'Shaughnessys, his widow and son pursued a dispute with Sir Theobald (Toby) Butler (qv) as far as the British house of lords in 1720.