Blanc was born in San Francisco, California to Russian-Jewish parents Frederick and Eva Blank, the younger of two children. He grew up in the neighborhood of Western Addition in San Francisco, and later in Portland, Oregon, where he attended Lincoln High School. Growing up, he had a fondness for voices and dialect which he began voicing at the age of 10. He claimed that he changed the spelling of his name when he was 16, from "Blank" to "Blanc", because a teacher told him that he would amount to nothing and be like his name, a "blank".

In the 1970s, Blanc gave a series of college lectures across the US and appeared in commercials for American Express. He also collaborated on a special with the Boston-based Shriners Burns Institute called Ounce of Prevention, which became a 30-minute TV special.  Throughout the 1980s, Blanc performed his Looney Tunes characters for bridging sequences in various compilation films of Golden-Age-era Warner Bros. cartoons, such as The Looney Looney Looney Bugs Bunny Movie, Bugs Bunny's 3rd Movie: 1001 Rabbit Tales, Daffy Duck's Fantastic Island, and Daffy Duck's Quackbusters. His final performance of his "Looney Tunes" roles was in Bugs Bunny's Wild World of Sports (1989). After spending most of two seasons voicing the diminutive robot Twiki in Buck Rogers in the 25th Century, Blanc's last original character was Heathcliff, in the early 1980s.  In the 1983 live-action film Strange Brew, Blanc voiced the father of Bob and Doug MacKenzie, at the request of comedian Rick Moranis.  In the 1988 live-action/animated movie Who Framed Roger Rabbit, Blanc reprised several of his classic "Looney Tunes" roles (Bugs, Daffy, Porky, Tweety, and Sylvester), but left Yosemite Sam to Joe Alaskey (who later became one of Blanc's regular replacements until his death in 2016). As Disney produced the film, the company had to obtain permission from Warner Bros. and other studios in order to feature the non-Disney characters in the movie. The film was also one of very few Disney projects Blanc was involved in. Blanc died just a year after the film's release. His final recording session was for Jetsons: The Movie (1990).

Was all of later work done for Warner Bros. ?
In the 1983 live-action film Strange Brew, Blanc voiced the father of Bob and Doug MacKenzie, at the request of comedian Rick Moranis.