Leeson, Joseph (c.1701–1783), 1st earl of Milltown , landowner, patron of the arts, was one of six surviving children – and apparently the only surviving son – of Joseph Leeson (qv), brewer and property developer, and his wife Margaret (daughter and co-heiress of Andrew Brice, esq., alderman and sheriff of the city of Dublin), of St Stephen's Green, Dublin. His date of birth is disputed but is most likely to be 11 March 1701. The grandiose style in which Leeson lived throughout his life was largely due to the fortune that his father had amassed through his brewing activities (located in St Stephen's Green), his prudent property speculation elsewhere in Dublin city, and his purchase of lands in at least nine Irish counties in the period c.1690–1740; at least one estate was purchased as a result of the Williamite confiscations. In 1741 Leeson was said to have inherited £50,000 in money and an annual income of £6,000 from his father. In c.1742 he purchased from John Graydon the Russellstown (later known as Russborough) estate in Co. Wicklow, demolished the existing house, and commissioned Richard Castle (qv) to build a new seat. In 1744, with his new house under construction, he set out on the Grand Tour. He stayed in Rome till October 1745 with the archaeologist Robert Wood (qv) and purchased antiquities, paintings, and furnishings. He had his portrait painted by Pompeo Batoni, the earliest recorded portrait of an English or Irish sitter by the artist. In March 1745 the merchant ship Augustus, which carried many of Leeson's precious goods, was seized by the French. It was partly this loss that prompted him to return to Italy in 1750 with his eldest son Joseph (1730–1801) and his nephew Joseph Henry of Straffan, Co. Kildare. Leeson rented a house off the Piazza di Spagna in Rome, and commissioned Batoni to paint further portraits.
When Leeson returned to Ireland in 1751 his country house was still unfinished and Francis Bindon (qv) completed the work shortly after the death of Castle in 1751. Russborough house was one of the most impressive neo-Palladian houses in Ireland in the latter half of the eighteenth century. The interior was filled with important objects that were ordered during Leeson's two visits to Italy, including copies of Guercino and Reni, architectural studies and capricci by Panini, oval marines by Vernet, decorative Florentine pictures, scagliola marble tables by Don Petro Belloni, bronzes by Soldani, and books on architecture. The house was further embellished with Italianate landscapes painted by George Barret (qv) and exotic woods brought from the West Indies. Emily Fitzgerald (qv), later duchess of Leinster, wrote in 1759 that the ‘house is really fine and the furniture magnificent, but a frightful place [i.e. sublime surroundings]. Mr Leeson carry'd us to see a very fine waterfall near it’ (Leinster correspondence, i, 76).
Leeson served (1743–56) as MP for the borough of Rathcormick, Co. Cork, and was high sheriff of Westmeath in 1756. He was made Baron Russborough (1756), Viscount Russborough (1760), and earl of Milltown (1763), and became a privy councillor in 1770. His elevation into the house of lords and rapid elevation within the peerage was most likely due to his wealth, social standing, and connoisseurship, rather than his political activities.
Leeson was a member of the Society of the Dilettanti and treated his collecting as a serious occupation. Sir Horace Mann commented on those occasions when Leeson offered huge sums for antiquities that had been recently excavated in Rome (and which were destined for the pope's collection). In Joshua Reynolds's painting ‘The parody of the school of Athens’ he is portrayed as Aristotle lecturing to a disciple. He was perhaps less suited to the lighter pastimes of the nobility and gentry. Richard Marlay wrote to Lord Charlemont (qv) in 1752 that ‘Leeson is to play Lothario [in the play ‘The fair penitent']. They say he will do it very ill’ (Charlemont manuscripts, 184).
He married first (20 January 1729) Cecilia (d. 1737), first daughter of Francis Leigh of Rathangan, Co. Kildare; they had two sons and one daughter. Leeson married secondly (1738/9) Ann, daughter of Nathaniel Preston of Swainstown, Co. Meath; they had at least one son and one daughter. He married thirdly Elizabeth, daughter of the Very Rev. William French; they had two sons and two daughters. The eldest son by the first marriage, Joseph (1730–1801), became 2nd earl of Milltown and travelled to Italy again in 1778. Brice (1735–1807), the second son, became 3rd earl. Joseph Leeson died on 22 October 1783. His estate was bequeathed in different proportions to a number of his children. His third wife, Elizabeth, dowager countess of Milltown, lived in a dower house that Leeson built for her on or near St Stephen's Green, till her death in 1842. Leeson was painted by Anthony Lee (qv) in 1735, who lived nearby on St Stephen's Green (NGI). Pompeo Batoni's portrait, dated 1744, is also in the NGI. A portrait miniature (c.1765) by Robert Wade, based on the Batoni portrait, is reproduced in Caffrey. Two engravings by C. Grignion after de Fesch were published in 1773. Leeson is possibly one of the six connoisseurs depicted in a group portrait painted by James Russell in 1762 (reproduced in Wilton). The Milltown bequest to the NGI c.1900 included much of Leeson's pictures and furniture.