Clements, William Sydney (1806–78), 3rd earl of Leitrim , landowner, and MP, was born in Dublin, second son among eight children of Nathaniel Clements (1768–1854), 2nd earl of Leitrim, and his wife Mary (d. 1840), co-heir of William Birmingham of Ross Hill, Co. Galway. Educated at private schools at Ham and at Beaconsfield, Buckinghamshire, he passed out of the Royal Military College, Sandhurst, in 1823. He was commissioned ensign in the 43rd Light Infantry (9 December 1824), served in Portugal (1826–8), was ADC to the lord lieutenant (1831–9), and retired from the army in 1855 as lieutenant-colonel. A bad fall from a horse in 1829 seriously damaged his knee and left him lame for the rest of his life.
After the death from tuberculosis of his elder brother Robert Birmingham Clements (1805–39), whig MP for Co. Leitrim (1826–30, 1832–9), William (styled Viscount Clements 1839–54), was returned unopposed at the 1839 by-election and sat as whig MP for Co. Leitrim until 1847, when the seat passed to his brother Charles Skeffington Clements (1807–77), MP 1847–52. William took a keen interest in political and economic matters; he strongly opposed the arms bill of 1843 limiting the public possession of arms, and maintained that ‘no people were so easily governed as his fellow countrymen’ (Duffy, 268). During the Famine (1845–9) he was chairman of the Mohill board of guardians in Co. Leitrim and was actively involved in relief schemes.
He succeeded to the earldom and as Baron Clements of Kilmacrenan (UK) on 31 December 1854. Owner of 50,000 acres in Donegal and estates in Galway, Leitrim, and Kildare, he lived mostly at Lough Rynn, Co. Leitrim, and at Mulroy, Co. Donegal, where he built a new house, known as Manor Vaughan, and laid out beautiful gardens. He invested heavily in land improvements, and abolished the communal rundale system on his estates. Unlike his father, who was renowned for his kindness, he was deeply unpopular with his tenantry. As he believed the land to be his alone, the notion of tenant right infuriated him and he sought to abolish the Ulster custom on his Donegal estates. Despite his threats, a public meeting at Milford on 21 January 1858 to protest against his treatment of his tenants was attended by 6,000 people. In the house of lords he generally voted with the tories after 1860 and condemned Gladstone's land act of 1870 as a dangerous encroachment on landlord rights; he also criticised Irish landlords for absenteeism. He brooked no interference with his privileges, concerned himself with the smallest details of his tenants' practices, and readily evicted those who made changes or improvements to their farms without his permission. He had a particular passion for planting trees and, to protect the young saplings, forbade the keeping of goats on his lands. Displays of independence by tenants usually moved him to fury, and he was alleged to have struck tenants on several occasions. In January 1858 during a dispute with the local priest, he outraged his catholic tenantry by seizing possession of a catholic church at Gortletteragh. This led to a tense confrontation between a strong force of troops and constabulary and a large crowd of local people that was defused only by the intervention of the catholic clergy. It seems, though, that Leitrim was oppressive to tenants regardless of their religion. From 1850 to 1878 rents on his estates rose by about 60 per cent, well above the average for the period.
Constantly engaged in litigation, he was also deeply unpopular with fellow landlords, who were appalled at the opprobrium he drew down on their class. He quarrelled bitterly with police officers and Dublin Castle officials, one of whom described him as ‘overbearing and insolent, bad tempered, so violent and disagreeable that he was an affliction to anyone with whom he came in contact’ (MacPhilip, 26). As part of a long-running dispute with the viceroy, Lord Carlisle (qv), in October 1863 he frustrated Carlisle's intentions to stay at a hotel on his land at Maam, Connemara, by packing it with local tenants at his own expense. This act led to his dismissal as JP for Co. Leitrim and Co. Donegal. Many folk legends grew up around his harshness and eccentricities, and it was widely rumoured that he used his powers to seduce his tenants' daughters. Frank Hugh O'Donnell (qv) repeated these claims in the house of commons after Leitrim's assassination and Michael Davitt (qv) included them in his Fall of feudalism in Ireland (1904). Those who knew Leitrim well maintained that they were simply vicious rumours, but the widespread belief that he was a sexual predator contributed to his notoriety.
At times Leitrim could be kind to tenants in distress, but even his efforts to improve the lot of his tenants were carried out in such a high-handed and insensitive manner that they usually offended those they were intended to help. The antipathy of his tenants towards him resulted in several unsuccessful attacks on his life, after which he usually travelled armed but refused the offer of police protection. His attempt to evict almost a hundred tenants at Lifford sessions in March 1878 led to firm plans for his assassination, which was probably organised by the Fanad Ribbon and Fenian societies. On 2 April 1878, while travelling by coach to his residence at Carrigart in north Donegal, he was ambushed by an armed gang at Cratloe Wood, near Mulroy Bay. In the first volley of shots his driver George Buchanan and clerk Jack McKim were fatally wounded, while Leitrim was shot in the arm and shoulder. Despite his injuries, he tackled his assailants, who then bludgeoned him to death with a shotgun butt. The attack was witnessed by Leitrim's groom and coachman, William Kincaid, and by a local blacksmith, Michael Logue, who were travelling behind in another vehicle. Because their horse had become lame, they lagged some distance behind Leitrim, which gave rise to much speculation that they were complicit in the attack.
Leitrim was buried in the family vault at St Michan's Church, Dublin; his funeral was marked by riotous scenes as an angry crowd tried to drag his coffin from the hearse. Despite the offer of a £10,000 reward for information about the crime, his killers – Michael McElwee, Neil Sheils, and Michael Heraghty – were never apprehended. A Celtic cross erected to their memory in Fanad in 1960 praised them for ending ‘the tyranny of landlordism’.
Leitrim never married, and was succeeded in his titles and estates by his nephew Robert Birmingham Clements (1847–92), who was a benevolent and popular landlord.