He grew up on Long Island, the eldest of seven children. He earned his bachelor's degree from Manhattan College in 1962, a master's from Colgate University, and a Ph.D. from the City University of New York.
He taught at Colgate University (1963), Hunter College (1964–1967), Lehman College (1965-1966) and the John Jay College of Criminal Justice (1966–1968). From 1968 until 2000, he taught at the University of Massachusetts Amherst where he became a Distinguished Professor of English. He taught at the Bread Loaf School of English in the 1980s and at the Bread Loaf Writers' Conference from 1982 until 1996. In 2000, he began teaching at Boston College, where he is the University Professor of English.
His published work includes five biographies and seven volumes of poetry, as well as several critical studies of modern poetry and a spiritual memoir, Thirty Days. In 2009, he was awarded the John Ciardi Award for Lifetime Achievement in Poetry. He has been honored with fellowships from the Guggenheim Foundation, the National Endowment for the Arts, and the National Endowment for the Humanities.
James Franco's film biopic of Hart Crane, The Broken Tower, released in 2012, is based on Mariani's biography of the same title.
- The Whole Harmonium: The Life of Wallace Stevens
- Epitaphs for the Journey: New, Selected and Revised Poems
- Gerard Manley Hopkins: A Life
- Deaths & Transfigurations: Poems
- God and the Imagination: Poetry, Poets, and the Ineffable
- Thirty Days: On Retreat with the Exercises of St. Ignatius
- The Broken Tower: A Life of Hart Crane
- The Great Wheel: Poems
- Lost Puritan: A Life of Robert Lowell
- Salvage Operations: New and Selected Poems
- Dream Song: The Life of John Berryman
- Prime Mover: Poems
- A Usable Past: Essays on Modern & Contemporary Poetry
- Crossing Cocytus: Poems
- William Carlos Williams: A New World Naked
- Timing Devices: Poems. Pennyroyal Press
- William Carlos Williams: The Poet and His Critics
- A Commentary on the Complete Poems of Gerard Manley Hopkins
- "Manhattan College Manhattan Magazine Spring 2010 AlumnoTes (sic) page 30 section 1962" (pdf). Manhattan College. 2010-03-31. Retrieved 2011-12-01.
- A biography of Paul Mariani provided by Poets.org
- The Gods Who Come Among Us In the Guise of Strangers—poem by Mariani
- Nick Ripatrazone. "Interview with Paul Mariani". The Fine Delight.