[3][4] Keiller was born on 10 August 1908 in North Berwick, Scotland, during a golf trip by her parents, Englishwoman Daisy Muriel Hoare and J. Wadsworth Ritchie, an American rancher.
[7][3] Keiller developed her collection of Dada and Surrealist art with the advice of the artist Roland Penrose.
[6] Her bequest to the Scottish National Gallery comprised over 170 artworks (including paintings, sculptures, prints and drawings) in addition to a library of manuscripts, rare books, and journals.
[6] Her third husband, Alexander Keiller, had used wealth from his family's marmalade business to pursue interests in archaeology, particularly the stone circles at Avebury in Wiltshire and the surrounding prehistoric landscape.
After his death in 1955, Gabrielle employed Isobel Smith to make archival records of Alexander's excavations in the 1920s and 1930s.
[13] From 1956 to approximately 1970, she assisted Rupert Bruce-Mitford in a study of the burial ship Sutton Hoo, taking photographs of the site.