Lowther, Sir Gerrard (Gerard) (1590–1660), lawyer and judge, was probably the natural son of Christopher Lowther of Penrith, Cumberland. He matriculated at Queen's College, Oxford, on 7 June 1605. He entered Gray's Inn in 1608 and was called to the bar in 1614. He was in Dublin as a member of the King's Inns in 1619. His marriage in 1621 to Anne, daughter of Sir Lawrence Parsons (qv), brought him into the ambit of Richard Boyle, the earl of Cork (qv), under whose wing Lowther would prosper for the next twelve years. He was attorney general of Munster from 26 November 1621 to 9 June 1623. After his father-in-law died in 1628 he appears to have succeeded him as Cork's chief legal adviser. He became second baron of the exchequer on 14 September 1628 and was knighted in 1631. As a justice of the assize he rode the Ulster circuit until 1641. On 29 April 1634 he became chief justice of the court of common pleas after Cork had offered Lord Deputy Wentworth (qv) £1000 to secure promotion for his client. He was sworn a member of the Irish privy council on the same day.
However, Cork was not to reap the expected dividends from his investment: Lowther would remain a loyal, almost too loyal, supporter of Wentworth for the next eight years. He played a key role in preparations for the plantation of Connaught in 1635, sat on the infamous commission for defective titles and in 1639 accompanied Wentworth to London to help him justify his imprisonment and dismissal of Lord Chancellor Adam Loftus (qv). Wentworth declared that he would always be in debt to him for the role he played in the overthrow of Loftus. On 6 July 1640 he was made attorney of the court of wards while also remaining chief justice. His chief residence was a rented house in Oxmantown, Dublin. He had land in Fermanagh and Wexford, and in early 1641 he was wealthy enough to lend £1,000 to the earl of Ormond (qv).
By early 1641 his closeness to Wentworth had become a major liability. On 27 February the Irish parliament accused Lowther and the rest of Wentworth's chief ministers of treason. On 4 March parliament had him arrested and ordered that he be dismissed from the council. The government bailed him but asked him not to attend council meetings. Meanwhile, parliament was drawing up articles of impeachment against Lowther and others, and in June it was reported that a majority was in favour of impeachment. However, parliament's desire for vengeance was sated both by Wentworth's blood and by a number of concessions made by the king. In October the start of a massive rebellion by the Irish catholics rendered such lofty constitutional issues superfluous. By the end of October Lowther appears again as a working member of the Irish council. He was formally acquitted of treason by parliament on 22 June 1642. In April and May 1644 he was in Oxford as part of the team representing the Irish council in negotiations with the catholic confederates before the king. At these negotiations Lowther was noted for displaying considerable animosity towards the confederates. In September 1646 he travelled to London to negotiate with parliament on behalf of the royalist lord deputy and by then marquess of Ormond. After the successful conclusion of these negotiations in 1647, whereby Ormond handed control of Dublin over to the English parliment, Lowther remained in London to serve the parliamentarian regime, which in March declared its confidence in his loyalty. In June 1648 he was made commissioner for raising money for the reconquest of Ireland; this project would occupy him for most of the next two years.
He was back in Ireland by March 1651, when he became commissioner of the peace for Leinster. He was president of the high court of justice (1652–4), one of the chief instruments of the Cromwellian regime in Ireland. Its role was to punish the perpetrators of the massacres of 1641. Among those whom he sentenced to death was Sir Phelim O'Neill (qv), the ringleader of the 1641 rebellion. Aided by the favour of Henry Cromwell (qv), he was confirmed as chief justice of the reconstituted court of common pleas in 1655 and was keeper of the privy seal in 1655–6. He died 3 April 1660 and was buried in St Michan's parish, Dublin, on 10 April. By 1634 his first wife had died, and he had married Margaret, daughter of Sir John King (qv). He had no children.