Mary Elizabeth Braddon (1835-1915) left a substantial number of unpublished manuscripts, letters, and notebooks at her death. These were inherited in the mid- 1990s by some of her descendents. They form what is known in this thesis as the Braddon Family Collection (BFC). The descriptive assessment of these manuscripts and papers is intended to shed light on the working methods of this prominent Victorian author. She also had a career as an actress in the 1850s, and as editor, critic, serial writer and hack journalist throughout the mid to late-nineteenth century and into the early twentieth century. These other facets of her life and work are borne out by the papers in the collection, and this assessment takes these aspects into consideration. This thesis is formed in two parts. First, the evaluation of some of her published and unpublished writing, which seeks to represent her within the context of Victorian literary and theatrical culture. Then, the Appendices with critical and editorial notes and introductions to the text in each section, which offer a full transcript of the unpublished BFC material, including two of the late Notebooks and a transcript of a published article by Braddon that appeared in the 'Idler' magazine in 1893. Access to this collection has provided an opportunity for a valuable and timely appraisal of this important Victorian writer. This thesis attempts to offer an initial critical assessment and contextual study of the material in the BFC and an appraisal of Braddon's work in the light of recent scholarship. The evidence in the collection accompanied by the critical evaluation of her work in this thesis will allow for a shift in focus away from how her career is typically defined, as a writer of sensation fiction. Grateful acknowledgement goes to the descendents of the Braddon and Maxwell families, without whose generosity this work would not have been possible.