In 1849, while working at a millinery in Cranbourne Alley, London,[15][16] Siddal made the acquaintance of Walter Deverell. Accounts differ on the circumstances of their meeting. One account is that she became acquainted with Deverell's father, who worked at the Government School of Design. Siddal showed some of her artwork to him, and he introduced her to his son.[17][18][19] In another account, William Allingham visited the milliner's to meet a woman he was acquainted with and admired; Siddal was the woman's co-worker and joined the pair on their walk home, as it was the women's usual practice to travel home from work together. Siddal made such an impression on Allingham that he recommended her as a possible model to his friend Deverell, who was struggling with a large oil painting based on the Shakespeare play Twelfth Night.[20] A third account has Deverell accompanying his mother to the millinery where he noticed Siddal in the back of the shop.[21] In any case, Deverell later described Siddal as "magnificently tall, with a lovely figure, and a face of the most delicate and finished modelling ... she has grey eyes, and her hair is like dazzling copper, and shimmers with luster."[22] Deverell subsequently employed Siddal as a model and introduced her to the Pre-Raphaelites.[23]
As with the other Pre-Raphaelites, Deverell took his inspiration directly from life rather than from an idealized classical figure. In his Twelfth Night painting, he based Orsino on himself, Feste on his friend Dante Gabriel Rossetti and Viola/Cesario on Siddal. This was the first time Siddal sat as a model.[24] According to William Michael Rossetti, Dante Gabriel's brother, "Deverell drew another Viola from her, in an etching for The Germ."[25][26] Elaine Shefer asserts that Deverell portrayed Siddal in A Pet and The Grey Parrot.[27]
William Holman Hunt painted her in A Converted British Family Sheltering a Christian Missionary from the Persecution of the Druids (1849–1850)[25] and Two Gentlemen of Verona, Valentine Rescuing Sylvia From Proteus (1850 or 1851).[25][28]
For John Everett Millais's Ophelia, Siddal floated in a bathtub full of water to portray the drowning Ophelia. Millais painted daily through the winter, putting oil lamps under the tub to warm the water. On one occasion, the lamps went out and the water became icy cold. Millais, absorbed by his painting, did not notice and Siddal did not complain. After this, she became ill with a severe cold or pneumonia. Her father held Millais responsible and, under the threat of legal action, Millais paid her doctor's bills.[29]
Siddal came to either embody or influence the Pre-Raphaelite ideals of feminine beauty.