Stagliano grew up in the Chicago suburbs, and attended high school from 1965 to 1969. He enrolled in college, but dropped out in 1969 for several semesters. He then went back to college and studied subjects including English, journalism, and engineering, before transferring to UCLA to major in economics. He originally planned to get an economics PhD and become a professor. He then switched to studying theater, playwriting, modern dance and jazz dance, partly because there were more women in those classes. He is of Italian ancestry with some of his grandparents from Florence.

In the 1970s, he wrote erotic fiction for a small newspaper, and did some softcore modeling. He made his debut in a hardcore pornographic film in an 8mm loop in 1974. In 1979, he was looking for dancing jobs in Hollywood. He replied to an advertisement in the Daily Variety looking for male strippers for the new Chippendales show. He performed with the group four or five nights a week for the next four years. In 1982, when he was 30, he began publishing a small pornographic magazine on newsprint, which he called Evil Angel.

Initially he had little knowledge of film making, but he made his first movie for $8,000 in 1983, titled Bouncing Buns, starring Stacy Donovan. For the next six years he made films for other companies to manufacture and distribute. In 1989, he started Evil Angel to sell his own films. The origin of the company's name dates back to when Stagliano was working as a stripper. "There was another guy in one of my shows named John. So this MC started calling me Evil John to differentiate us. This was when I was doing Dracula and chains. At the same time I had a girlfriend who called herself Angel when she did strip shows. She was a very nasty girl and I suggested that she call herself Evil Angel. She didn't, but I loved the name and wound up using it for my company."

The first Evil Angel film was Dance Fire, filmed in 1988 by Stagliano, starring himself, Trinity Loren, Brandy Alex Andre and others. In 1989, he produced "The Adventures of Buttman," the first in a popular series which is credited with sparking the "gonzo" adult film genre. These films involved highlighting the female buttocks, with actors often licking, kissing and playfully biting the female behind. Stagliano has stated that a scene showing Tracey Adams' buttocks inspired him to make the Buttman series of films. The clip shows Adams on her hands and knees with her rear end stuck high in the air. "The shot only lasted a couple of seconds," says Stagliano, "but I knew then what I wanted to do." Early Stagliano productions had little to no anal sex in them and were critically acclaimed for the showcasing of his buttocks fetish. Later Buttman films included numerous anal sex scenes, often featuring Stagliano himself. In the 1990s, Stagliano became one of the most successful figures in American pornographic films.

Stagliano was in a relationship with pornographic Actress Krysti Lynn (aka Shawna Yager) during 1993. She was driving Stagliano's Acura Legend when she died on December 7, 1995, in an accident in Calabasas.

In 1997, Stagliano tested positive for HIV. To date, medication has kept the virus in check.

Stagliano was described by U.S. News and World Report magazine in 1998 as "the nation's leading Director of hard-core videos."

From October 2004 through February 2008, Stagliano produced and directed a Las Vegas show called Fashionistas based on his porn film of the same name. In 2008, he won the 'Best Director - Video' award for Fashionistas Safado: Berlin. ("Safado" is a Portuguese word meaning lewd or salacious.)

He married former porn star Tricia Devereaux (Karen Stagliano) in 2008. Stagliano espouses a libertarian political philosophy, and has been a significant financial contributor to the Cato Institute and the Reason Foundation, both libertarian think tanks.

On July 16, 2010, a federal trial began in Washington, D.C. with Stagliano as defendant and after three days all charges were dismissed. Judge Richard J. Leon stated, "I hope the government will learn a lesson from its experience," and called the evidence linking Stagliano to the production and distribution of the DVD videos "woefully insufficient". Although he dismissed the charges on the grounds of insufficient evidence, the judge cited the "difficult, challenging and novel questions" raised in the case against Stagliano, questions concerning extant federal obscenity-statutes, the internet, free speech, and the rights of Criminal defendants. He stated that he hoped "[higher] courts and Congress will give greater guidance to judges in whose courtrooms these cases will be tried."

In her essay "Crackers and Whackers: The White Trash of Porn," which among other things brings into relief the heritage of bawdy songs, the related oral culture of joke telling, and the "bawdy, farcical character" of early stag films in modern porn, Constance Penley, exclaiming that after its golden era passed, porn became "wonderfully trashy again," asserts that John Stagliano did for anal fetishism what Woody Allen did for neurosis, pointing out that, "as in so many stag films," Buttman is the "butt of the joke" since, "seeking the perfect shot of a woman's perfect ass," the character "gets mugged, evicted, bankrupted, rejected, and ridiculed –  all in his single-minded quest for perfection."

The suit against Stagliano went into forced arbitration and the plaintiff had her deposition taken, but on 29 September 2014 Summers dropped her lawsuit. According to Stagliano's attorney, Paul Cambria, “[Summers] had no case. I took her testimony and when I was done I could not see any possible way for her to succeed.”