Caulfeild, William (1665–1737), MP and justice of king's bench, was eldest son of Capt. Thomas Caulfeild (d. 1691), landowner, of Donamon, Co. Galway, and his wife Anne, eldest daughter of Charles, 2nd Viscount Moore, of Drogheda. The family estate comprised lands in Co. Galway and Co. Roscommon. In 1692, shortly after succeeding his father, William was elected MP for Tulsk, Co. Roscommon, which he continued to represent in later parliaments (1692–3, 1695–9, 1703–13, 1713–14). Although whig in politics, in 1695 he defended Sir Charles Porter (qv), the lord chancellor, against accusations of favouring catholics; the following year he signed the association for the protection of William III (qv). In September 1700 he entered the Middle Temple and was called to the Irish bar in 1704, becoming in December 1708 second serjeant, a poorly paid position of greater political than legal weight. In 1710 he introduced in the commons what became the act ‘to prevent the maiming of cattle’. During the hougher campaign in Galway and Roscommon (1711–13), he was involved in local counter-measures against nocturnal meetings and the killing of livestock, and vehemently accused catholic secular clergy of complicity in agrarian crime.
When the tories took office in 1711 he was dismissed as second serjeant, but following the death of Queen Anne (August 1714), he was appointed by the whig administration as prime serjeant (8 December 1714), an office considered a secure stepping-stone to the bench. In summer 1715, as anxieties over possible Jacobite invasion spread in Ireland, he was active in having catholic meetings proclaimed. Appointed second justice of the king's bench (3 June 1715), he continued to exercise an important influence on behalf of government through his attendance as a judge in the Irish house of lords. He was involved in frantic negotiation (December 1715) with MPs opposing the government supply bills. One of the few recorded incidents in his career on the bench occurred in June 1718, when he carried out a ‘most minute investigation’ into the lifestyle and dress of women arrested in Dublin on suspicion of living as members of a religious order; he concluded that no breach of the penal code could be cited against them. He played a role in attempts to resolve the constitutional crisis of 1719 over the appeals jurisdiction of the British house of lords in Ireland. In the 1719 parliamentary session he assisted with the indemnity bill for Irish protestant dissenters. Harried by chronic ill health from the later 1720s, he was absent from the bench from 1730, retiring in 1734. He died 24 August 1737 in Donamon.
He married (1691) Lettice, fourth daughter of Sir Arthur Gore (d.1697), first baronet, of Newtown, Co. Mayo. They had three daughters and five sons, three of whom were MPs, Thomas (1688–1747), MP for Tulsk (1715–27, 1741–7); Toby (1694–1740), MP for Tulsk (1727–40); and St George Caulfeild (1697–1778), MP for Tulsk (1727–51) and chief justice of the king's bench (1751–60).