Walsh was born Charles H. Walsh in Los Angeles, California; his parents worked for the Foreign Service, and Walsh lived in East Africa, India and Indonesia before the age of ten. His family returned to the United States 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 to act professionally.
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, such as Betsy's Wedding, Congo, and playing Paul Newman's son in Nobody's Fool, as well as making television appearances in shows like the police drama Brooklyn South, The Twilight Zone and more recently, Everwood.
In 2003, Walsh landed the role of Sean McNamara on 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 TV movie.
On November 12, 2007, it was announced that Walsh would star in the remake of The Stepfather. He would revive the role made famous by Terry O'Quinn. Production for the film is set to begin in March or April 2008.