The picture collection at Erddig is, rightly, most celebrated for its collection of 'Servant' portraits (which actually include those of estate staff, and a butcher-cum-publican). These were painted in two different periods: by John Walters of Denbigh for Philip Yorke I (1743–1804), between 1791 and 1796; and by William Jones, in 1830, for Simon Yorke II (1771–1834). Philip Yorke I also adapted the portrait of an otherwise unknown John Hanby at the age of 25 (who was probably a white man) into an imaginary portrait of one of a couple of dimly-remembered black coachboys of an earlier owner of the house, John Meller (1665–1733).

There is more to Erddig's collection, however, than just the 'servant' portraits. Among the other portraits are commissioned works, such as those by Francis Cotes, Thomas Gainsborough, Francis Wheatley as well as a curiosity, a portrait probably by Charles Jervas, updated by Gainsborough. There are also several extraneous portraits acquired for the collection; these include works by Marcus Geeraerts the younger, Jacob Fransz. van der Merck and Godfrey Kneller. Erddig also has what is evidently a consciously put together picture collection, even if many of the pictures in it are only what we would now recognise as copies, works 'in the style of' other artists, or by minor masters. The very obscurity of one or two of these last, however, is what lends them their interest. The "Landscape with Huntsmen", for instance, is apparently signed calligraphically P. Vandervoorde 171[6?]. No such artist is now identifiable, but it seems possible that there may once have been a letter before the 'P', and that the painting may therefore be by the same artist as that of a similar picture recorded in 1912 in the Matsvanszky collection in Vienna, on which the signature was read as J. van der Voort and the date as 1714. This would make him identifiable with Joseph van der Voort, who is recorded as the Dean of the Antwerp Painters' Guild from 1734 to 1735. By such recognitions, the oeuvre of forgotten artists can be reassembled. After the National Trust acquired Erddig in 1973, most of these pictures were hung in the Drawing Room, which it redecorated and hung as a picture cabinet, as it had been described in 1923.

The early eighteenth-century portraits are mostly hung in the former Entrance Hall, despite its conversion into a Music Room in the later part of the century, while the later eighteenth-century and nineteenth-century portraits are primarily in the Dining Room. In some ways the most interesting group of portraits is to be found in the crosswise Gallery, which was recorded in 1732 as 'hung with ye Sibylls, all [whole] lengths'. By 1787, these were so decayed that they were sold off to the steward. Since then the crosswise Gallery has been hung with portraits inherited in 1770 by Philip Yorke I from a rich maternal uncle, James Hutton of Newnham, Hertfordshire and Park Lane. A number of these are by Dutch artists, and have as subjects major figures of the United Provinces (now the Netherlands) and the Thirty Years' War. These seem likely to have been acquired by, and to have descended from, the two lesser Shropshire figures, Major Henry Meoles and Captain Meoles, both painted in 1649 by Jacob Fransz. van der Merck. A number of the Old Masters were also inherited from James Hutton.

There is a bowdlerised adaptation by the Honourable Elizabeth Cust, "A Young Woman with a Basket of Doves", a variant of Guido Reni's much-copied "Salome Holding the Head of John the Baptist", which has recently been recovered for the Brownlow collection at Belton.

Some of the later Yorkes were also themselves occasional amateur artists, but very few of their works are – or ever have been – shown in the house. Those that are, hang in what the Yorkes themselves called 'The Failures Gallery', a passage used by the servants, leading to the Chapel. However, William Haydon Fuge's portrait of "Philip Yorke II (1849–1922), as Mayor of Wrexham "also hangs here.

From the First World War onward, the family fortunes, estate, house, and contents, diminished and decayed – accelerated by subsidence caused by old coal-mine workings. However, the last of the Yorkes of Erddig, Philip Yorke III (1905–1978 – the owners of Erddig had alternated between Simons and Philips since the eighteenth century), whose chief pleasure – after a failed attempt at the priesthood – was theatricals, was determined to save 'this unique establishment for which my family have foregone many luxuries and comforts over seven generations.' The National Trust was the obvious recourse, but negotiations took six and half years, and only reached a successful conclusion thanks to £120,000 from the National Coal Board, in compensation for the damage caused by mining under the house, which then also ceased, and to £1 million from the sale of a small parcel of land in the property boom – the one thing that Philip Yorke would never do, was to take advantage of the similar boom in the price of pictures and antiques. In 1973 the handover was accomplished.