Haig was born Sidney Eddy Mosesian in Fresno, California, and was raised in an Armenian community. His father, Haig Mosesian, was an electrician. Haig's career began somewhat by accident. As a young man, his rapid growth interfered with his motor coordination, prompting him to take dancing lessons. At the age of seven years, he was a paid dancer in a children’s Christmas show, and later joined a vaudeville revival show.
Haig also displayed musical talent particularly for the drums, prompting his parents to buy him a drum set, on which he mastered a wide range of music styles, including swing, country, jazz, blues and rock and roll. He found it easy to earn money with his music, and signed a recording contract one year out of high school. Still a teenager, Haig went on to record the single "Full House" with the T-Birds in 1958, which shot to #4 on the charts.
When Haig was in high school, the head of the drama department was Alice Merrill, who encouraged him to pursue an acting career. Merrill had been a Broadway actress who maintained her contacts in the business. During his senior year, a play was produced in which Merrill double cast the show, to have one of her Hollywood friends assess the actors in order to select the final cast.
The Hollywood contact who saw Haig perform was Dennis Morgan, a big musical comedy star from the 1940s, who chose Haig for a prominent role in the play. Two weeks later, he returned to see the show and advised Haig to continue his education in the San Fernando Valley and consider acting as a career. Two years later, Haig enrolled in the Pasadena Playhouse, the school that trained such noted actors as Robert Preston, Gene Hackman and Dustin Hoffman. He later moved to Hollywood with longtime friend and Pasadena Playhouse roommate Stuart Margolin.
Haig's first acting job was in Jack Hill's student film at UCLA titled The Host, which launched Haig's more-than-four decade acting career in over fifty films and 350 television episodes. He became a staple in Hill's films, such as Spider Baby, Coffy and Foxy Brown.
Haig was a regular player for producer-director Roger Corman. He appeared in George Lucas' THX 1138 (1971) and the James Bond film Diamonds Are Forever (1971). His television credits include appearances in such programs as Batman, Gunsmoke, Get Smart, Mary Hartman, Mary Hartman (55 appearances), Mission: Impossible (at least eight appearances in eight different roles as a villain), Charlie's Angels, Jason of Star Command, Buck Rogers in the 25th Century, The Dukes of Hazzard, Automan, MacGyver and The A-Team (in which he played a jailed motorcycle gang leader) and Emergency! (again as a motorcycle gang leader).
Haig retired in 1992, feeling typecast: "I just didn't want to play stupid heavies anymore. They just kept giving me the same parts but just putting different clothes on me. It was stupid, and I resented it, and I wouldn't have anything to do with it". Haig did not work in acting for five years, instead training and becoming a certified Hypnotherapist.
During this time, he was offered the role of Marsellus Wallace (later to be played by Ving Rhames) in Pulp Fiction, Quentin Tarantino's second film. At the time, Haig was concerned that low budget television had been ruining his career and, at seeing the shooting script and the short number of days dedicated for each locale, he passed on the project. He has said that he always regretted this decision. Then, in 1997, Tarantino wrote the part of the judge in Jackie Brown specifically for Haig.
In 2003, Haig starred in Rob Zombie's debut film House of 1000 Corpses, as Captain Spaulding. The role revived Haig's acting career, earning him a "Best Supporting Actor" award in the thirteenth Annual Fangoria Chainsaw Awards, and induction into the Horror Hall of Fame. His image as Captain Spaulding has become iconic in today's horror genre. Haig reprised his role as Spaulding in Zombie’s sequel to House of 1000 Corpses, entitled The Devil's Rejects.
For this film, he received the award for "Best Actor" in the 15th Annual Fangoria Chainsaw Awards, as well as sharing the award for "Most Vile Villain" at the First Annual Spike TV Scream Awards with Leslie Easterbrook, Sheri Moon and Bill Moseley as The Firefly Family. He was also nominated as "Best Butcher" in the Fuse/Fangoria Chainsaw Awards, but lost to Tobin Bell's Jigsaw from Saw II.
Recently, Haig reunited with Rob Zombie once again, albeit briefly, in the director's Halloween remake, in the role of cemetery caretaker Chester Chesterfield. Sid Haig also reprised the role of Captain Spaulding in Rob Zombie's animated film The Haunted World of El Superbeasto. Haig most recently starred in the independent horror film Brotherhood of Blood, which was shot in Baton Rouge, Louisiana, he also appeared in The Lords of Salem (reuniting him with Rob Zombie), Hatchet 3 and Devil in My Ride.
Haig starred in the documentary film Vampira: The Movie, which based on Maila Nurmi's cult character Vampira.