Walsh's first role was in a television movie called Soldier Boys with James Earl Jones. He then landed a role in the movie Loverboy and a regular role on the television series Kate & Allie. In 1989, he started using the name Dylan Walsh professionally. He continued to work in films including Betsy's Wedding, Nobody's Fool, Congo, The Stepfather, and Secretariat, and guest starred the television series Brooklyn South, The Twilight Zone, and Everwood.

In 2003, Walsh landed the role of Sean McNamara on the television series Nip/Tuck, after being approached by series creator Ryan Murphy in a coffee shop. Murphy remembered him from his role in Nobody's Fool and in a television movie. Walsh also appeared on the series Unforgettable.

Walsh was married to Actress Melora Walters from 1996 to 2003, with whom he had two children, born in 1996 and 1997. The couple later divorced and Walsh married Actress Joanna Going on October 10, 2004, with whom he has a daughter born in 2003. On December 15, 2010 Walsh announced he had filed for divorce. Walsh also has a daughter born in 2011, and a son born in 2013.

Walsh was born Charles Hunter Walsh in Los Angeles, California. His maternal grandfather, Frank P. Haven, was a managing Editor of the Los Angeles Times. His parents worked for the Foreign Service—they met in Ethiopia. As a result, Walsh lived in East Africa, India, Pakistan and Indonesia as a boy. His family returned to the United States when he was ten years old and settled in Virginia, where Walsh began acting in high school. He graduated from the University of Virginia in 1986 with a degree in English. After graduating from college, Walsh moved to New York City to act professionally.