Davies-Colley's career as a surgeon spanned almost thirty years. On graduating in 1907, she became a house surgeon under Maud Chadburn (with whom she was to live and work for twenty-five years) at the New Hospital for Women, founded by Elizabeth Garrett Anderson; renamed the Elizabeth Garrett Anderson Hospital after Garrett Anderson's death in 1917, it is now part of the University College London Hospitals. She then became demonstrator in anatomy at the London School of Medicine and surgical registrar at the Royal Free Hospital. In addition to her work at the South London Hospital, in later life she was also a surgeon at the Marie Curie Cancer Hospital and senior obstetrician at the Elizabeth Garrett Anderson Hospital.