Marshall has a Bachelor of Arts from Victoria University of Wellington, a BA with Honours and a Masters with Honours from the University of Waikato. She completed a PhD titled The female voice in the Assembly of ladies: a 'volume without contours' at the University of Sydney.^[1] Marshall then joined the faculty of the University of Otago, rising to associate professor in 2018 and full professor in 2022.^[2][3]

Marshall identified a previously unknown edition of Chaucer's works from 1807, and was invited to write a biography of Chaucer by Wiley/Blackwell. This discovery shows that Chaucer's life has been used to "uphold conservative white attitudes".^[3][4]

Marshall has received two Marsden grants. In 2009, the grant "A new paradigm of medieval literary anonymity" explored how anonymity is conscious feature of medieval literature rather than reflective of a lack of authorial individualism. Marshall found that anonymity was a literary convention used by marginalised people, including women, to express dissent.^[5] Marshall was an associate investigator on a 2011 Marsden grant "The machinery of transcendence: unattended moments in the Modernist tradition", which was led by Professor Chris Ackerley. This grant explored the relationship between medieval traditions and Modernist aesthetics.^[5]

In 2023, inspired by medieval works such as the Book of Kells and the Lindisfarne Gospels that reflect where they are from, Marshall initiated a collaborative project with Otago Art Society to create a "Book of Otago". Community groups, schools, artists and writers were invited to submit a page for the book about what Otago means to them. The pages were exhibited at the Otago Art Society during November and December 2023, and will be bound into a published book.^[6][7]

Marshall practices and teaches calligraphy, to assist students in understanding the skills required to produce the manuscripts they are studying.^[4] Marshall teaches courses on monsters and monstrosity in medieval literature, medieval misogyny and those who fought against it, and also teaches a class in a surveying course, covering the Hereford Mappa Mundi.^[8]

• Simone Celine Marshall (30 August 2020). "The Poetical Works of Geoffrey Chaucer in the Nineteenth Century: Social Influences on Editorial Practices". Romantic Textualities: literature and print culture, 1780-1840. 0 (23): 218. doi:10.18573/ROMTEXT.80. ISSN 1748-0116. Wikidata Q124159175.
• S. C. Marshall (22 April 2011). "The 1807 Edition of the Poetical Works of Geoffrey Chaucer". Notes and Queries. 58 (2): 183–186. doi:10.1093/NOTESJ/GJR053. ISSN 0029-3970. Wikidata Q123773134.
• Marshall, S. (13 June 2007). "Engagement Theory, WebCT, and academic writing in Australia". International Journal of Education and Development Using Information and Communication Technology. 3 (2). ISSN 1814-0556. Wikidata Q124159197.
• Simone Celine Marshall (2007). "Manuscript Agency and the Findern Manuscript". Bulletin of the Modern Language Society of Helsinki. 108 (2): 339–349. ISSN 0028-3754. JSTOR 43344292. Wikidata Q124159253.
• Simone Celine Marshall; Carole M. Cusack (2017), The medieval presence in the modernist aesthetic: unattended moments, vol. 11, Wikidata Q124159254