Her second biography Margaret Fuller: A New American Life (2013) is a richly detailed account of Margaret Fuller, the 19th-century author, journalist, and women's rights advocate who perished in a shipwreck off New York's Fire Island.
Her first book, published in 1984, was The Cost of Loving: Women and the New Fear of Intimacy, which examines the impact of the feminist movement on its followers.
Marshall is particularly interested in uncovering and exploring the lives of women who have been forgotten by traditional historians and biographers.
Supported by grants and teaching, she worked on the book The Peabody Sisters for nearly 20 years, reading original letters and documents as well as delving into the newspapers and literature of the era.
In a conversation in Radcliffe Magazine with author Margot Livesey, Marshall spoke about the connection between the two biographies: "I wrote The Peabody Sisters partly to prove that the New England Transcendentalists included other brilliant women besides Fuller.