Kavanaugh founded Relativity Media after briefly serving as a consultant to other small businesses and venture capitalists. In the late 1990s, he asked his Father for a $50,000 loan to start his own hedge fund; his Father declined, but this did not dissuade Ryan, whose aim was to use mathematical tools to connect financing and movie projects in a more efficient manner than traditional Hollywood Finance. At Relativity, he created what is now known as "the model", a monte carlo model designed to predict the odds of a given film being successful. No film at Relativity is given a green light unless the model predicts a high probability of profitability. During Relativity’s first year of operation, Kavanaugh executed what was considered to be an innovative Finance deal for Marvel Studios which led them to create the Marvel Cinematic Universe. Kavanaugh went on to structure Business deals for such companies as: Sony, Universal, Warner Brothers, among many others. Kavanaugh has acquired a number of assets, including the marketing and distribution operations of John Malone's Liberty Media/Starz film unit Overture Films, and reaching a first of its kind TV pay deal with Netflix.

Kavanaugh currently resides in Malibu, California. In 1998, he married makeup Artist Tracy Tanner. In 2011, he married ballet Dancer Britta Lazenga. They divorced in 2014. The bachelor party was thrown by actors Leonardo DiCaprio and Bradley Cooper. In 2015, Kavanaugh married model Jessica Roffey. He is a member of the Wilshire Boulevard Temple.

Kavanaugh was honored with the 2009 Hollywood Producer of the Year Award at the 13th Annual Hollywood Awards Gala and Daily Variety published a special issue honoring Kavanaugh as a "Billion Dollar Producer". In 2010, The Hollywood Reporter bestowed the Leadership Award to Kavanaugh and the Daily Reporter dedicated a special issue in his honor as a "Billion Dollar Producer". He was named Variety's Showman of the Year, 2011.

Kavanaugh was 21st on Fortune's 40 Under 40 Most Influential People in Business in 2010 and in Forbes’ Future 400: Ones To Watch. He was named a "Top Thinker" by Esquire. He also serves on the boards of other charitable foundations such as Cedars-Sinai Board of Governors and as Chairman of The Art of Elysium.

Kavanaugh was honored with the 2011 Entertainment Industry Award by the Anti-Defamation League, a group committed to fighting anti-Semitism and bigotry of all kinds. The award is given to individuals who demonstrate leadership and extraordinary innovation in the entertainment industry. Kavanaugh serves as the Chairman of the Board for The Art of Elysium, an organization that encourages actors, artists and Musicians to voluntarily dedicate their time and talent to children who are battling serious medical conditions.

Kavanaugh led a group acquiring FreeHand, a premium dog food manufacturer best known for its work rescuing homeless dogs. He intends to integrate FreeHand into the activities of Relativity, including a TV series based around building a dog food company and increased awareness of dog rescue, and is one of the fastest growing dog food companies in the US. It has been renamed Dog For Doog, and Kavanaugh remains majority shareholder along with Michael Buble, Chelsea Handler, Snoop Dog. Kavanaugh remains chairman of the board and the largest shareholder. Kavanaugh has launched a show on Saturday mornings called Save My Shelter with Dog for Dog which runs every Saturday at 9am. Dog for Dog has quickly become one of the fastest growing Dog food companies in the United States and Canada. He invested $25 million in luxury leather maker nuMobilia in 2012, Kavanaugh is a significant investor in music game creator BandFuse: Rock Legends.

Hacking of Sony accounts in late 2014 revealed that Kavanaugh had sent an email to actresses including Natalie Portman and Scarlett Johansson, telling them to join him in taking action against what he saw as increased antisemitism which could end up as "another Hollacast" [sic].

On July 30, 2015, the company filed for Chapter 11 bankruptcy. However, the studio plans to go through with the release of Kidnap and Masterminds. Shortly thereafter, Ryan Kavanaugh with partner Joe Nicholas purchased back the entire company, Relativity, and reduced the debt by almost 800 million dollars, but later Joe filed to have Ryan move to Chapter 7, because the losses, unpaid bills and mounting lack of transparency was too difficult for Mr. Nicholas to deal with on an ongoing basis.

Kavanaugh recently became involved in dog rescue through his acquisition of FreeHand, saying that "We hope this will become a staple of Hollywood, and if you are not involved in this, then you’re not promoting social good amongst the animal world." He has been recognized for his charitable work by organizations including Cedars-Sinai Medical Center, whose Board of Governors honored him as the sole winner of the 2010 Hollywood Humanitarian Award; the Sheriff’s Youth Foundation, which presented him with its Community Champion Award in recognition of his outstanding dedication to inner-city young people; and by First Star for his dedication to improving life for child victims of abuse and neglect.