Among the most popular exhibits was a substantial display of works of art organised and underwritten by the railway magnate William Dargan.

This gift included about 223 paintings, 48 pieces of sculpture, 33 engravings, much silver, furniture and a library, and prompted construction from 1899 to 1903 of what is now called the Milltown Wing, designed by Thomas Newenham Deane.

[1][5] At around this time Henry Vaughan left 31 watercolours by J. M. W. Turner with the requirement that they could only be exhibited in January, this to protect them from the ill-effects of sunlight.

Though modern lighting technology has made this stipulation unnecessary, the gallery continues to restrict viewing of the Vaughan bequest to January and the exhibition is treated as something of an occasion.

George Bernard Shaw also made a substantial bequest, leaving the gallery a third of royalties of his estate in gratitude for the time he spent there as a youth.

The same year the gallery was once again given some of the contents of Russborough House when Alfred Beit donated 17 masterpieces, including paintings by Velázquez, Murillo, Steen, Vermeer and Raeburn.

In the 1990s a lost Caravaggio, The Taking of Christ, known through replicas, was discovered hanging in a Jesuit house of studies in Leeson Street in Dublin by Sergio Benedetti, senior conservator of the gallery.

Unlike the previous two extensions, this new wing has street frontage and the English architects Benson & Forsyth gave it an imposing Bowers Whitbed, Portland stone façade and grand atrium.

The design originally involved demolishing an adjoining Georgian terrace house and its ballroom mews; however, the Irish planning appeals authority, An Bord Pleanála, required that they be retained.

The next two phases of the project involved the replacement of the Milltown Wing roof, followed by an extensive upgrade of the fabric and services of the two buildings whilst reclaiming their original period elegance.

The collection has about 14,000 artworks, including about 2,500 oil paintings, 5,000 drawings, 5,000 prints, and some sculpture, furniture and other works of art.