Schwartz was born to a Jewish family in 1976 in Providence, Rhode Island, the son of Steve and Honey Schwartz. His parents were both toy inventors at Hasbro, working on the development of toys such as Transformers and My Little Pony, until they went on to start their own company. Schwartz grew up on the east side of Providence, Rhode Island with a younger brother, Danny, and a younger sister, Katie. Schwartz always had ambitions of being a Writer since early childhood.

He attended Providence's private Wheeler School, a coeducational independent day school, for 11 years, graduating with the class of 1994.

In 1995, Schwartz attended film school to study screen and television writing at the University of Southern California (USC). He became a member of the Pi Kappa Alpha fraternity, as well as President of the chapter, and got to see what it's like "behind the gated communities and big mansions" of Southern California which would later provide fodder for his pilot The O.C.

The O.C. became an instant teen favorite when it debuted on the Fox Network in August 2003. The show popularized its setting, Orange County, and led to copycats like MTV's reality show Laguna Beach: The Real Orange County and the Bravo documentary series The Real Housewives of Orange County. The show became well known for its music, chosen by Schwartz according to his own musical tastes and designed to reflect who the characters were, bringing the general public an awareness of indie rock bands like Death Cab for Cutie, Bloc Party and Rooney. He has said that he partially based The O.C. character Seth Cohen on his own Jewish upbringing. Schwartz was nominated for a Writers Guild of America Award for the pilot as well as a People's Choice Award. The O.C. was named "Guilty Pleasure of the Year" by VH1. In 2007, after 4 seasons The O.C. was canceled due to a significant ratings drop.

Schwartz has worked on his share of stalled projects. In 2004, he worked as a script Doctor on the J. J. Abrams Superman screenplay that Warner Bros. eventually tossed. He sold a pilot to Fox called Alphabet City, a drama about a New York tabloid but it was never produced. He also worked on a drama for Fox called Athens described as an "OC" companion but it was never produced.

In 2005, Paramount signed Schwartz to adapt and direct John Green's young adult novel Looking for Alaska with Producer Mark Waters.

It was revealed in late August 2006 that Schwartz would develop and executive produce a drama pilot for The CW, based on the popular book series Gossip Girl by Cecily von Ziegesar. Like The O.C., Gossip Girl is a satirical approach of teenagers in a wealthy upbringing. Gossip Girl has become a very popular show for The CW.

In 2007, Schwartz signed a three-year, seven-figure overall deal with Warner Bros. TV to write and exec produce with Chris Fedak an hourlong high-concept action comedy called Chuck for NBC about twenty-something spies and was described in press releases as "in the vein of Grosse Pointe Blank". The plot revolves around a normal guy who downloads the entire CIA and NSA databases into his head.

On September 20, 2008, Schwartz married Jill Stonerock in Santa Barbara, California. Actress Rachel Bilson, who portrayed Summer Roberts on Schwartz's show The O.C., was the maid of honor at the wedding. They have two daughters, of whom Bilson is the godmother.

In Spring 2009, Schwartz launched "Rockville CA", a web-series on TheWB.com that follows young 20-somethings at a fictional rock club in Los Angeles. There are twenty indie band performances in the episodes, including Lykke Li, The Kooks and Kaiser Chiefs.

In September 2011, it was announced by The CW that Schwartz and Stephanie Savage had been selected to develop the television adaption of Candace Bushnell's The Carrie Diaries, a prequel to the original Sex and the City television series. The series, set in the 1980s, will follow character Carrie Bradshaw during her years in high school.

In January 2012, it was announced The CW had ordered a pilot for new drama titled Cult, result of collaboration with Stephanie Savage and Len Goldstein. This is Schwartz and Savage's fourth series on the network.

While at USC, Schwartz tried out stand-up comedy at a talent show in front of five hundred people but was "disabused of [the] notion very quickly." In his sophomore year he wrote an autobiographical screenplay about his senior year in high school called Providence as a homework assignment for school. He entered his screenplay into a contest for the prestigious Nicholson Award in Screenwriting, the highest honor awarded to undergraduates, and won. Unfortunately, the prize was quickly revoked; to be eligible he had to be in his junior year at the time. Schwartz says "I dropped it in a box – I was a sophomore. And I got a call over the summer saying I'd won, and I'd won five thousand dollars. I was like, 'This is awesome!' Then they called back, like, the next day and said you had to be a junior to enter and not a sophomore, so they were rescinding it. I was pretty pissed." Nevertheless, with help from connections through his fraternity, he generated interest in Hollywood to buy his screenplay. In 1997, Sony's TriStar Pictures bought his first screenplay in a bidding war for a deal guaranteeing $550,000 and worth up to $1 million while he was still a junior in college. It was never made.