Armstrong's book Stories and the Brain: The Neuroscience of Narrative was published in May 2020 by Johns Hopkins University Press (hardback, paperback, and e-book). This neuro-phenomenological analysis of our embodied cognitive capacity to tell and follow stories is a sequel to his book How Literature Plays with the Brain: The Neuroscience of Reading and Art (Johns Hopkins UP, hardcover and e-book 2013; paperback 2014; Slovenian translation, Arabic and Chinese translations in progress).
His other books include The Phenomenology of Henry James (U of North Carolina P, 1983), The Challenge of Bewilderment: Understanding and Representation in James, Conrad, and Ford (Cornell UP, 1987; e-book 2018), Conflicting Readings: Variety and Validity in Interpretation (U of North Carolina P, 1990; Spanish and Arabic translations), and Play and the Politics of Reading: The Social Uses of Modernist Form (Cornell UP, 2005). The opening chapter of Conflicting Readings was awarded the William Riley Parker Prize for an Outstanding Article in PMLA . His chapter on Nostromo in The Challenge of Bewilderment won the Twentieth Century Literature Prize in Literary Criticism.
Armstrong has also prepared several critical and scholarly editions of major modern novels. His Norton Critical Edition of E. M. Forster's novel A Passage to India was published in September 2020. He has previously published two Norton Critical Editions of Joseph Conrad's novella Heart of Darkness (5th edition; W. W. Norton, 2017; 4th ed., W. W. Norton, 2006). The 2017 revised edition features a newly established text based on the first English book publication as well as a substantially revised critical apparatus. He has previously produced a Norton Critical Edition of E. M. Forster, Howards End (W. W. Norton, 1998). Armstrong has also completed a scholarly edition of Henry James's posthumously published, unfinished novel The Ivory Tower for the Cambridge University Press series of James's collected fiction (in press, anticipated publication 2022). He is currently at work on a scholarly edition of Howards End for the Cambridge University Press edition of Forster's fiction.
Before coming to Brown as Dean of the College in 2001, Armstrong was Dean of Arts and Sciences at SUNY-Stony Brook and Humanities Dean at the University of Oregon. He has also taught at the University of Virginia and Georgia Tech and has been a visiting professor at the University of Copenhagen and the Free University of Berlin. He is also a member of the visiting faculty of the Institute for Doctoral Studies in the Visual Arts (IDSVA).
Armstrong has held fellowships from the Alexander von Humboldt Foundation and the National Endowment for the Humanities. He also received a grant from the Teagle Foundation to chair an inter-institutional working group that wrote a white paper on "The Open Curriculum: An Alternative Tradition in Liberal Education." Past president of the Joseph Conrad Society of America, Armstrong is a member of the editorial boards of the Henry James Review, Conradiana, and Modern Fiction Studies.