Cusack, James (c.1590–c.1659), lawyer and politician, was third son of Edward Cusack and Elizabeth Aylmer, both of whom belonged to prominent Old English catholic families of the Pale. The Cusacks had a distinguished history of governmental service, and James appeared destined to follow in this tradition, entering Middle Temple on 15 September 1619. Having successfully completed his studies, Cusack found employment in London searching for royal titles to lands in Ireland. About this time he married Frances, daughter of William Talbot (qv), and received a grant of land at Grenanstown, Co. Meath, from his brother-in-law, Sir Robert Talbot (qv). In 1633 the lord-deputy, Thomas Wentworth (qv), established the commission for defective titles in Dublin, with Cusack as its secretary, a post he held until 1641, one of the few catholic officeholders during the reign of Charles I. Cusack's tenure of office proved difficult, and he was effectively replaced in 1636, after the appointment of the protestant Sir Philip Percival (qv) as joint-clerk.
He attended the 1634 parliament as a member for the borough of Old Leighlin in Co. Carlow (due to Wentworth's influence), and was returned for the same constituency in 1640, as well as for the Donegal borough of Ballyshannon. Cusack eventually opted for Ballyshannon and was replaced in Old Leighlin by another catholic, Thomas Davills. He quickly emerged as a leader of the catholic group in the commons, sitting on numerous committees, including the committee for examining the controversial Connacht plantation. He also helped formulate the articles of impeachment against the lord chancellor, Sir Richard Bolton (qv); the lord chief justice, Sir Gerald Lowther (qv); the bishop of Derry, John Bramhall (qv); and Sir George Radcliffe (qv). After the outbreak of the Ulster rising on 22 October 1641, Cusack and the other catholic MPs attempted to act as mediators. The lords justices, however, frustrated their efforts by proroguing parliament on 17 November, and Cusack joined the insurgents shortly afterwards. On 22 June 1642 he and forty other catholics were expelled from the commons; he was declared an outlaw five months later.
Cusack was a member of the provisional council established by the rebels in June 1642, and was elected to the first confederate supreme council by the general assembly held in Kilkenny at the end of the year. He also served as confederate attorney-general and judge of the admiralty, concentrating throughout the 1640s almost exclusively on legal rather than political matters. As a result he successfully avoided any involvement in the confederate factional struggles that developed from 1643 onwards. In September 1646 the papal nuncio, GianBattista Rinuccini (qv), seized control of the government in Kilkenny, imprisoning members of the previous administration for advocating a peace treaty with the lord lieutenant, James Butler (qv), marquess of Ormond. The treaty rejected by the nuncio included the recommendation that Cusack be appointed as chancellor of the exchequer or king's attorney in a new royalist administration. None the less, Cusack served the clerical regime as a commissioner of public revenue while remaining committed to the idea of a settlement with Ormond. When civil war erupted in May 1648 he sided with the nuncio's enemies, attended the final general assembly (September), and took a direct part in negotiating religious terms with Ormond. The confederates and royalists signed a second peace treaty in January 1649, and in November 1649 Ormond appointed Cusack as attorney-general and chief judge of the admiralty court.
The collapse of Irish catholic fortunes after the Cromwellian invasion destroyed Cusack's political and legal career, and he was among those excepted from the general pardon granted on 12 August 1652. Nothing is known of his subsequent activities, although surviving records note the death of a ‘Mr Cusack’ on 27 June 1659. Cusack had certainly died by 1664, when it fell to his eldest son Thomas to petition Ormond (unsuccessfully, it seems) for the restoration of family estates. He was survived by his wife (d. 1688), three sons (Thomas, William, and Nicholas) and one daughter (Ellinor).