Before working in the porn industry, she first worked at a German bakery,a Jiffy Lube, and later a tax and retirement firm.

While studying to be a pediatric nurse in Orange County, a classmate who was an exotic dancer introduced Leone to John Stevens, an agent who in turn introduced her to Jay Allen, a photographer for Penthouse magazine. When picking a name for her adult career, she has said that Sunny is her real name and Leone was picked by Bob Guccione, former owner of Penthouse magazine. She posed for Penthouse magazine, and was named Penthouse Pet of the Month for the March 2001 issue, followed by a feature in the Holiday 2001 edition of Hustler magazine as a Hustler Honey. She has appeared in other magazines including Cheri, Mystique Magazine, High Society, Swank, AVN Online, Leg World, Club International and Lowrider,^[17][18] while her online credits include ModFX Models, Suze Randall, Ken Marcus and Mac & Bumble. Her pictorial credits also include working with stars like Adriana Sage, Jenna Jameson, Jelena Jensen and Aria Giovanni.

In 2003, she was declared the Penthouse Pet of the Year and also starred in the video Penthouse Pets in Paradise alongside Tera Patrick and Kyla Cole. In 2005 Adam & Eve appointed her as their West Coast Internet Sales Representative.

That same year, Leone signed a three-year contract with Vivid Entertainment with which she transitioned into the world of hardcore pornography, stating that she would only do lesbian scenes. Her first movie released was titled Sunny and was released in December 2005. Her next movie, Virtual Vivid Girl Sunny Leone, was the first interactive title for Leone, who was the first Vivid Girl to make such a movie. Taking only four days to film, the movie won her her first AVN Award (Best Interactive DVD). She followed this with Sunny Loves Cher, which featured her first on-screen squirting,and The Female Gardner co-starring Mikayla Mendez and Daisy Marie.

Leone's last two movies under her contract with Vivid were It's Sunny in Brazil, which was filmed in Brazil. and The Sunny Experiment also starring Monique Alexander and Brea Lynn. The movies were released in October and December 2007 respectively.

In May 2007, upon re-signing her contract with Vivid for another six films, Leone agreed to perform for the first time with men on camera, but exclusively with her fiancé, Matt Erikson. That summer she also received breast augmentation, and shot her first movie under the new contract titled Sunny Loves Matt. The movie led to her to be nominated for three (out of six) AVN awards in 2009 in addition to being a choice for Female Performer of the Year. She followed up her first boy-girl title with The Other Side of Sunny in October 2008, which would be the last time she would perform with Erikson.

In January 2008, Leone revealed that she was no longer exclusive to Erikson, and had done scenes with other actors, most notably Tommy Gunn, Charles Dera, James Deen and Voodoo. In August of that same year, she announced the launch of her own studio, Sunlust Pictures, with Daniel Weber as her partner. With her new venture Leone plans to write, direct and create her own brand of adult movies with Vivid Entertainment as her distributor. Her first independent production, The Dark Side of the Sun, was released in March 2009, and was debuted at the Erotic Heritage Museum in Las Vegas. In June 2009, she held a casting call in Las Vegas for her second independent production titled Sunny Slumber Party (released September 2009).

No longer exclusive to Vivid, Leone has started working with other studios and performers since 2009. She has managed to leverage her online popularity by striking deals with firms like PPPcard, AdultPokerParty.com, Brickhouse, Flirt4Free, Totemcash and Imlive to sell and distribute her content over the internet and other media.She won the "Web Babe of the Year" at the 2008 Xbiz Awards. Her websites and business interests are run under her banner company Leone L.L.C.

In addition to her film career, Leone has been part of the Vivid Comedy Tour, and has modelled for the Vivid Footwear collection. Leone has also participated in events like the Vivid/ClubJenna Lingerie Bowl and Vivid's Hot Rod Night. Doc Johnson launched a pocket pal^{[clarification needed]} in 2006 moulded to her vagina, and in 2008 released the Sunny Leone Exciter vibrator. Control MFG currently uses Leone's image along with other Vivid girls to market their line of skateboards. She is paired with Gab Ekoe, one of the Team Control riders. She also indicated that she plans to launch her own line of lingerie and other Sunny-branded products including a diamond jewellery line.

In September 2009, an iPhone application consisting of a collection of non-nude photos, some videos and a porn star-penned blog was approved by Apple for sale in the iTunes store, making it the first officially sanctioned application featuring a porn star. By February 2010, the app had been removed by Apple from the store.

Leone was voted #13 on Genesis magazine's "Top 100 Porn stars" list, #34 on Desiclubs.com's Top 50 Coolest Desis of 2004, and one of the "40 under 40" ranking on AVN Online magazine. In 2010, she was named by Maxim as one of the 12 top female stars in porn.