Regarded as one of the foremost scholars and collectors of his generation this gift is of immense importance. Sir Denis was born in London and studied at Eton and Oxford before pursuing his passion for the history of art. His father John Fitzgerald Mahon (1858-1942) was the son of Sir William Vesey Ross Mahon 4th Bt. (1813-1893) of Castlegar, Co. Galway and his mother (Alice Evelyn Browne) was the daughter of the 5th Marquess of Sligo. While studying history at Oxford, he became acquainted with Kenneth Clarke, then at the Ashmolean Museum. Clarke recommended that he indulge his interest in art history by studying with Nikolaus Pevsner and it was Pevsner who suggested to the young scholar that he study the art of Guercino.
In addition to his remarkable achievements as a scholar and collector, Sir Denis is remembered for his tireless advocacy of museums.He campaigned vigorously and successfully to maintain free access at a time when Government was embarking on a policy of insisting on charges.
In 2010, Sir Denis Mahon, who passed away earlier this year, presented his personal library and archive to the Gallery. This remarkable gift, considerably enhances the research resources relating to European art available in Ireland. Of Irish descent, Sir Denis had a long and close association with the Gallery having donated a gift of eight outstanding seventeenth-century Baroque pictures to the collection.This wonderful gift is a reflection of his fondness for Ireland and the esteem in which he held the National Gallery of Ireland.
Relocating this cornucopia of books and documentation was a challenging undertaking. The books and documentation, which represent decades of research and scholarship, had been stored over the five floors of Mahon’s Knightsbridge home, No. 33 Cadogan Square. Between January and May 2010, an NGI team, including library, archive and conservation staff, organised and packed the entire contents. Close to 1000 bankers boxes were transported back from London to Merrion Square.