Cassells is the author of four books of poetry. His first book, The Mud Actor, was a National Poetry Series selection for 1982. The second collection of poems was Soul Make a Path Through Shouting (1994), received the Poetry Society of America's William Carlos Williams Award and was nominated for a Pulitzer Prize. His third volume, Beautiful Signor, was published in 1997. In 2003 he published Down From The Houses of Magic: New and Selected Poems.

His awards include a Lannan Literary Award, the William Carlos Williams Award, a Lambda Literary Award, and a Pushcart Prize. Cyrus Cassells has received the Peter I.B. Lavan Younger Poet Award of the Academy of American Poets and fellowships from the Lannan Foundation, the Rockefeller Foundation, and the National Endowment for the Arts. He has taught at the College of the Holy Cross and Northeastern University. He is an associate professor of English at Southwest Texas State University, and lives in Austin.