Efron was born in San Luis Obispo, California and later moved to Arroyo Grande, California. His father, David Efron, is an engineer at a power plant, and his mother, Starla Baskett, is a former secretary who worked at the same power plant as Efron's father. Efron had a self-described "normal childhood" in a middle class family, and has a younger brother, Dylan. Efron is of Jewish ancestry and is an agnostic, having never been religious. He has said that he would "flip out" if he got a 'B' and not an 'A' in school, and that he was a "class clown." Efron's father encouraged him to begin acting when Efron was eleven. He subsequently appeared in theater productions at his high school, worked in a theater called The Great American Melodrama and Vaudeville, and began taking singing lessons. Efron performed in plays such as Gypsy, Peter Pan, Or The Boy Who Wouldn't Grow Up, Little Shop of Horrors, and The Music Man. Efron was recommended to an agent in Los Angeles by his drama teacher, Robyn Metchik (the mother of actors Aaron Michael Metchik and Asher Metchik). He was later signed to the Creative Artists Agency.
Efron graduated from Arroyo Grande High School in 2006, and was then accepted into the University of Southern California, but he deferred his enrollment while he worked on film projects. He plans to return at some time. Efron also attended Pacific Conservatory of the Performing Arts, a community college located in Santa Maria, California, which provided him with the opportunity to perform as a "young player" during the years of 2000 and 2001.
Efron owns an apartment and has two dogs, Australian shepherds named Dreamer and Puppy. He also has a Siamese cat named Simon.
On January 15, 2008, Efron was hospitalized at Cedars-Sinai Medical Center in Los Angeles for an emergency appendectomy.
Zac Efron was also on the Forbes Celebrity 100 list in 2008, as number 92 with an estimated earning of $5.8 million from June of '07 to June of '08.
Vanessa Hudgens confirmed, in an October 2007 interview with Teen Magazine, that she and Efron had been dating since the filming of High School Musical.