Thompson (Thomson), William (1726–98), portrait painter and author, was born in Dublin, the eldest of a large family. His father lived off a small paternal inheritance and looked after the agency of several estates for absentee landlords, but still found it difficult to support his large extended family. William, whose surname more often appears as Thomson, was educated as a scholar. He was sent to Mullingar, where he studied Greek and Latin with the Rev. Dr Ross, a Church of England clergyman, but his wish to join the ministry was marred by a shortage of money to pay for his studies. However, he showed a talent in art, and attended painting classes with Francis Bindon (qv), a portrait painter (he painted many portraits of Dean Swift (qv)) and architect, recently returned to Ireland from Italy. Having practised in Dublin for a short while, Thompson moved to Portarlington on 9 May 1752, but the following year he left for England in the hope of finding a patron, and never returned. His portraits were considered technically correct but dull and hence, much to his disappointment, he never found the patronage he sought.
He married Elizabeth Baynes, second daughter of Thomas Baynes esq. of Houses, Great Samford, Essex, on 12 July 1756. She was a wealthy woman and many years his senior. He hoped to travel to Italy but soon found himself in debt, and a spell in the king's bench prison about 1770 put paid to that idea. He painted a portrait of James Stephen, the author of Considerations on imprisonment for debt (1770), which was engraved in mezzotint by William Dickinson and published by Thompson in Warwick Court, London. Indeed Thompson himself was vociferous in his objections to prison sentences for debt. As a member of the Society of Artists, of which he was secretary for a time, he took part in their exhibitions, showing forty-three portraits between 1760 and 1782. He showed just one portrait with the Free Society of Artists, in 1782. He painted a portrait of Cadwallader Blayney, 9th Baron Blayney (1720–82), lord lieutenant of Co. Monaghan and grand master of the freemasons, of which an anonymous mezzotint engraving, published some time after 1766, is in the NGI. When the Society of Artists split into factions he published anonymously a pamphlet, The conduct of the Royal Academicians while members of the Society of Artists from 1760 to their expulsion in 1769 (1771). It received little attention.
His wife died 1 September 1786 and on 11 May 1787 he married a widow, Mrs Comyns, an educated woman who ran a boarding school at Brompton, where he had taught drawing. He was associated with the famous Mrs Theresa Cornely's Assembly Rooms at Carlisle House, Soho Square, where he was chairman of the debating society and also founded a school of oratory. His fallacious address earned him the nickname ‘Blarney’ Thompson. It appears that he was accused of embezzling his second wife's fortune, and by order of the court of chancery he was directed to recover it. He died suddenly 3 December 1798, while engaged in preparations for the publication of a book he had written some years earlier. The book, An enquiry into the elementary principles of beauty in the works of nature and art (1798), was published soon afterwards, and perhaps best highlights his proficiency in the classics.