On June 4, 1978, Robin Williams married his first wife, Valerie Velardi. Their son Zachary Pym "Zak" Williams was born on April 11, 1983. During Williams's first marriage, he was involved in an extramarital relationship with Michelle Tish Carter, a cocktail waitress whom he met in 1984. She sued him in 1986, claiming that he did not tell her he was infected with the herpes simplex virus before he embarked on a sexual relationship with her in the mid-1980s, during which, she said, he transmitted the virus to her. The case was settled out of court. Williams and Velardi divorced in 1988.

On April 30, 1989, he married Marsha Garces, Zak's nanny, who was several months pregnant with his child. They had two children, Zelda Rae Williams (born July 31, 1989) and Cody Alan Williams (born November 25, 1991). In March 2008, Garces filed for divorce from Williams, citing irreconcilable differences.

Williams married his third wife, graphic designer Susan Schneider, on October 23, 2011, in St. Helena, California. Their residence was Williams's house in Sea Cliff, a neighborhood in San Francisco, California.