Colthurst, Sir John Conway (c.1743–1787), 2nd baronet and landowner, was eldest of five sons of John Conway Colthurst (d. 1775), 1st baronet, and his wife Charlotte (d. 1774), third daughter of Thomas FitzMaurice, 1st earl of Kerry. His father, MP for Doneraile (1751–60), Youghal (1761–8), and Castlemartyr (1769–75) in Co. Cork, was a supporter of the 1st and 2nd earls of Shannon, Henry (qv) (d. 1764) and Richard Boyle (qv) (d. 1807). Colthurst himself stood for the borough of Mallow in the 1783 general election, though Shannon refused to endorse him. His failure in the election, where he came bottom of the poll, led him to renounce his family's hereditary attachment to the Shannon interest.
Colthurst's enmity towards the Boyles was reinforced by their respective attitudes towards the anglican clergy's right to collect the tithe; Richard Boyle had received strong clerical electoral support since the 1770s, and Colthurst sought to embarrass him by campaigning on the tithe issue. Lingering animosity, magnified by his 1783 election failure, saw Colthurst's actions embody the links between nascent Rightboyism and some landowners in Co. Cork, while simultaneously demonstrating how personal differences could inflect party and class divisions.
Colthurst was notorious for clashing with local clergy on his estates in Muskerry, Co. Cork, and Dingle, Co. Kerry. From the late 1770s he selectively refused to pay the tithe on his estates in West Muskerry (Ballyvourney and Clondrohib), encouraging others to do the same; in north-west Cork his combination with other local landlords forced the local clergyman to resign when his annual income plummeted from £200 to less than £10. Prominent among those agitating for reform of the tithe system in Cork, Colthurst was a founder of the embryonic ‘Cork Farmers' Club’, established in 1775 in Blarney. Colthurst and Arabella Jeffereyes (qv), sister of John Fitzgibbon (qv), became popular with the Rightboys for their encouragement of withholding the tithe. Though Jefferyes was more a champion of the popular cause, Colthurst's actions were directed more by disappointed ambition and personal animus; J. B. Bennet, a contemporary chronicler of events, described Colthurst as a man ‘of much cunning, of great suppleness and speciousness of manners, and of an affected zeal for the public interest’ (quoted in Dickson, 448).
Dominick Trant (qv), Fitzgibbon's brother-in-law, published a pamphlet examining Rightboy disturbances in Cork, Considerations on the present disturbances in the province of Munster (Dublin, 1787). An acolyte of Richard Woodward (qv), bishop of Cloyne, a staunch defender of the established church and constitution, Trant noted the importance of an anonymous local landowner to the disturbances. Colthurst, taking offence at this clear insinuation that he was as an unofficial ‘gentleman’ leader of the movement, challenged Trant to a duel. After successfully avoiding the authorities, the combatants managed to meet just outside Bray, Co. Wicklow, on 14 February 1787. Colthurst had duelled on a number of occasions in the past and took John ‘Bully’ Egan (qv), another celebrated duellist, as his second. Trant, largely unfavoured as well as short-sighted, took Richard Hely-Hutchinson (qv) as his second (Egan and Hely-Hutchinson had duelled in 1783, in circumstances pertaining to the general election in Cork). After four exchanges of fire Trant mortally wounded Colthurst, who died five days later on 19 February 1787 in Bray.
Colthurst never married. His younger brother Nicholas (d. 1796), succeeded him as 3rd baronet, and renewed links with the Boyle family as MP for St Johnstown, Co. Longford (1783–90) and Clonakilty (1792–5).