Dennis was born on September 17, 1939, in St. Louis, Missouri. He attended Oberlin College (1957—58) and the University of Chicago (1958—59) and ultimately attained his bachelor's degree from the University of Minnesota in 1961. He pursued graduate education at the University of California, Berkeley, where he received his doctorate in 1966. Dennis has had a long career in education at the State University of New York at Buffalo, where he worked as an assistant professor from 1966 to 1971, an associate professor from 1971 until 1976, and a professor of English from 1976 to 2001. In 2001, he became an artist in residence at the State University of New York at Buffalo, a post he still holds.

His first book of poetry, House of My Own, was published in 1974. Over the next two decades, Dennis published five more books of poetry: Climbing Down (1976), Signs and Wonders (1979), The Near World (1985), The Outskirts of Troy (1988), and Meetings with...