He was married to Mary Beth Hurt for three years from 1971 to 1982, still married to Mary Beth, he fell in love with ballett-dancer Sandra Jennings and start to live with her. When filming The Big Chill in South Carolina, Sandra Jennings stayed with the father of her unborn child Alexander Devon (*1984). Because he wasn't divorced that time, William told Sandra they had "a spiritual marriage". In December 1982 he obtained divorce from his former wife and went back to New York 1983 with Sandra.

Shooting Children of a lesser God William met Marlee Martin and began a relationship with the actress.

In 1989 Sandra Jennings put William Hurt in a trial in New York's supreme court, to prove that she and William had entered into a "common law" marriage, because his attitude towards Sandra had cooled off.
Sandra Jennings failed to get counsel fees, accountant's and appraiser's fee and the court also denied Sandra's request for child support, because William had made tax-free, voluntary child support before.
(Jennings vs. Hurt, 554 NYS2d 220)

The same year William Hurt married Heidi Henderson, the daughter of musican Skitch Henderson, who became the mother of William's sons Sam and William jr.  They divorced in 1992.

William Hurt's last known serious relationship was with Sandrine Bonnaire, who gave his only daughter Jeanne birth.