Williams grew up in Newark, New Jersey and graduated from Columbia High School in Maplewood. He later studied at Bucknell University and the University of Pennsylvania. During this time, he spent five lonely months in Paris trying to write before realizing he knew nothing about poetry, noting in a New York Times article, that "It was an incredibly important time, not much happened and yet my life began then. I discovered the limits of loneliness." He returned to Pennsylvania determined to learn something of poetry and began his writing career. He launched himself as a vehement anti-war poet at during the U. S. conflicts in southeast Asia. His first collection, Lies, was politically engaged; 1972 saw his first collection of explicitly antiwar poems.

He began teaching in 1975, first at a Y.M.C.A. in Philadelphia, later at Drexel University, and then at the Franklin & Marshall College.

He met his present wife, Catherine Mauger, a jeweller of French descent, in 1973, and they have a son who is now a noted painter. Williams also has a daughter, born in 1969, from an earlier marriage.

He is known for a poetic style involving long lines of unrhyming free verse. His subjects are modern and predominately urban, his voice that of an 'outspoken liberal.' Anti-war themes pervade his entire writing career. He was highly critical of the Bush administration and the Iraq war, stating in 2005 that "The unreasonableness of war, the killing of children, drives me to distraction. My moral system grows out of this. There has never been a moment in my life when I felt we were in so much danger. I am a father and a grandfather. I have three grandsons. I am afraid for them." Williams is an acclaimed translator, notably of Sophocles' Women of Trachis and Euripides' The Bacchae in the classic canon and more contemporarily, of the Polish poet Adam Zagajewski and the French writer Francis Ponge.

He has won nearly every major poetry award. Flesh and Blood won the National Book Critics Circle Award. Repair (1999) won the 2000 Pulitzer Prize for Poetry, was a National Book Award finalist and won the Los Angeles Times Book Prize. The Singing won the National Book Award in 2003. In 2005, he was awarded the Ruth Lilly Poetry Prize.

Since 1996, he has taught in the creative writing program at Princeton University, and he divides his time between Princeton and France.