Agron was born in Savannah, Georgia, and raised in San Antonio, Texas, and San Francisco, California, the daughter of Mary (née Barnes) and Ronald S. Agron, a general manager of Hyatt hotels. Due to her father's career, Agron said she and her family lived in different hotels growing up. She has a younger brother, Jason. Her father was born to a Jewish family, while her mother converted to Judaism. Agron attended Hebrew school and had a Bat Mitzvah. Agron's paternal great-grandparents were Jewish immigrants from Eastern Europe, and according to her, their original surname, Agronsky, was altered by Ellis Island officials.
When she was 15, she found out that her father had multiple sclerosis. In an interview for Cosmopolitan, she revealed, "Quite a bit changed after that. At that age, you don't see mortality in your parents." The disease caused her parents' relationship to fall apart, and they decided to separate, which was devastating for her and her younger brother. She stated, "I had to play therapist to my family... be the glue. Those kinds of things I'm not ready to speak about yet."
Agron attended Burlingame Intermediate School and Burlingame High School, where she was in the Homecoming Court, and played the part of Marty in Grease; she was also involved in set design, costumes, and painting. She has been dancing since the age of three, focusing mainly in jazz and ballet, and later began hip-hop dancing. Agron then fell in love with musical theater, and often performed in local and school productions. She played Dorothy Gale in The Wizard of Oz in fifth grade, and began teaching dance as a teenager. She says she was not "popular" in the stereotypical sense in high school, though she had many friends from different cliques around the school. As a teenager, Agron worked at a local boutique, where she "became enthralled with fashion," and was on her high school's yearbook committee.
Agron has appeared on television series such as Shark, Close to Home, CSI: NY, Numb3rs, and Veronica Mars. She appeared as Harper in a 13-episode series of short films, It's a Mall World, directed by Milo Ventimiglia, that aired on MTV. She then had a recurring role on the second season of Heroes as Debbie Marshall, the captain of the cheerleading squad at Costa Verde High School. After this role, she was only offered horror films that included nudity, and turned them all down.
Agron's most notable role to date is as Quinn Fabray, a high school cheerleader, on the Fox comedy-drama series Glee. Agron was the last primary actor to be cast, having won the role only days before the pilot began filming. Agron said in a 2009 interview pertaining to her casting session, "I nearly bailed on my audition for the show. I was so nervous." Before being cast as Quinn, the show's producers wondered if she appeared too innocent. Agron said in an interview, "They told me to come back with straight hair and to dress sexier. Later that week, I started work." She auditioned with Frank Sinatra's "Fly Me to the Moon". Quinn is described by Agron as Rachel Berry's (Lea Michele) enemy, and "terrible, the meanest girl." The character was originally conceived as the antagonistic queen bee head cheerleader, a departure from Agron's actual high school experience. The role saw Agron nominated for the Teen Choice Award for Female Breakout Star in 2009. She and the other cast members were awarded the Screen Actors Guild Award for Outstanding Performance by an Ensemble in a Comedy Series in 2010, and were nominated in the same category the following year.
On July 23, 2012, it was reported that Agron was going to appear less frequently in Glee's fourth season, being demoted to a guest star. Agron's character only appeared on three episodes: "Thanksgiving", "Naked", and "I Do". Agron returned in the fifth season for the two-part 100th episode special, "100" and "New Directions". Agron announced she would return to Glee for its final season after the show's music producer, Alex Anders, shared a photo of Agron recording music at Capitol Records. She featured as a main cast member in two episodes, "Homecoming" and "Jagged Little Tapestry", and made a cameo on the series finale "Dreams Come True".
In 2007, Agron appeared as Dyanna in the action-thriller film T.K.O., directed by Declan Mulvey, alongside Samantha Alarcon, Daz Crawford, and Christian Boeving. She also appeared as Megan in the comedy film Skid Marks. She also appeared as Kyle's Girl in the short comedy film, Rushers, which won the 2007 Methodfest Film Festival Audience Award for Best Short Film, written and directed by Joey Boukadakis. She also appeared as Dianna in the short comedy film Dinner with Raphael, which premiered at the 2009 Vail Film Festival, and was written and directed by Joey Boukadakis. She had a small role as Sadie in the comedy film Celebrities Anonymous, directed by Dennis Hemphill Jr., alongside Lindsay Zir and Joey Kern. In 2010, she appeared in the supporting role of Minnow Hayes in the romantic comedy The Romantics. That same year, she played Natalie in the musical drama film Burlesque. She also appeared in Bold Native, a film about animal liberation. In 2010, Agron auditioned for the role of Gwen Stacy for the reboot of the Spider-Man films, The Amazing Spiderman, but lost out on the role to Emma Stone.
In 2011, Agron appeared as Alice in the horror thriller The Hunters, and as Sarah Hart in the science-fiction action thriller I Am Number Four. Agron appeared in the concert film of Glee, Glee: The 3D Concert Movie. She then played Belle Blake in the film The Family, opposite Robert De Niro, Tommy Lee Jones, and Michelle Pfeiffer. The film was released on September 13, 2013, and received mixed to negative reviews. The Family debuted at #2 in its first weekend with $14.5 million. Critics praised Agron's performance. Tom Medley wrote, "[Agron] gives the best performance in the film as a really sexy teenager coming of sexual age." Writing for The Huffington Post, Zorianna Kit said, "De Niro, Pfeiffer and Jones all brought 100% to their roles. Glee actress Dianna Agron was the stand-out here, shining as the daughter who was falling in love for the first time, while defending her family from total annihilation by the mafia."
In 2015, Agron appeared in the political thriller Zipper as Dalia, the intern of a lawyer who is running for office. The film also starred Patrick Wilson, Lena Headey, and John Cho. Zipper premiered on January 27, 2015 at the Sundance Film Festival, and was released on August 28, 2015 in a limited release and through video on demand. Agron then co-starred in the romantic comedy-drama Tumbledown, alongside Jason Sudeikis and Rebecca Hall, which premiered at the Tribeca Film Festival. That same year, she had her first lead role as Sarah Barton in the drama film Bare, which also premiered at Tribeca. It was written and directed by Natalia Leite and follows a young girl living in a small desert town in Nevada as she becomes romantically involved with a female drifter. Paz de la Huerta, Chris Zylka, and Louisa Krause also starred in the film.
Agron is part of the main cast of The Crash, alongside Frank Grillo, AnnaSophia Robb, Minnie Driver, and Ed Westwick, which was released on January 13, 2017. She also stars in Novitiate, portraying a young nun in a convent, opposite Melissa Leo and Margaret Qualley, which is set to premiere at the 2017 Sundance Film Festival. Agron is set to co-star in the thriller Headlock, with Andy García, Justin Bartha, and James Frain, and will portray the lead in the drama Hollow in the Land.
Agron made her stage debut in the play McQueen, based on the life of the designer Alexander McQueen (Stephen Wight). She portrayed the female lead, Dahlia, a fan who breaks into the designer's home to steal a dress and is caught by McQueen, The fantasy-based play was written by James Phillips for the fifth anniversary of McQueen's death. The play ran from May 12 to June 6, 2015 at London's St. James Theatre. Agron was unable to reprise her role as Dahlia in the West End theatre re-run due to "filming commitments".
Several songs performed by Agron as Quinn Fabray on Glee have been released as singles, available for digital download, also featured on the show's soundtrack albums. Agron made her musical debut at the end of the episode "Showmance", performing Dionne Warwick's "I Say a Little Prayer". "I Say a Little Prayer" charted in the UK Singles Chart at 125. Quinn's next solo was in the episode "Throwdown", performing The Supremes' "You Keep Me Hangin' On". The song charted in the UK Singles Chart at 166. The song was released on Glee: The Music, Volume 1. The Wall Street Journal editor Raymund Flandez was critical of Quinn's cover of "You Keep Me Hangin' On", which he called "thin and jarring". She performed a rendition of James Brown's "It's a Man's Man's Man's World" in the episode "Funk". The song charted in the Canadian Hot 100 chart at 73, UK Singles Chart at 94 and in the Billboard Hot 100 chart at 95.
In season three, Agron sang her first solo number since the first season, "Never Can Say Goodbye" by The Jackson 5, which received mostly positive reviews. Jen Chaney of The Washington Post gave the song a "B-", and said it "worked much better than every track that preceded it" because it adapted the song to the show "instead of trying to out-Jackson Jackson." Entertainment Weekly's Joseph Brannigan Lynch called it "a nice summation of her character's journey, but not vocally impressive enough to justify listening to outside of the episode" and gave it a "B" rating. Crystal Bell of HuffPost TV described it as a "blah performance", but Kate Stanhope of TV Guide said it was "sweet and reflective." Erica Futterman of Rolling Stone wrote that it was "a tune well-suited for Quinn's sultry voice and the flipped meaning she gives the lyrics", and TVLine's Michael Slezak had a similar take: he gave it an "A" rating and called it a "remarkably lovely fit" for her voice. She has also sung in many cast group songs and duets.
In 2011, when asked about if she is interested in a solo album, Agron said that she is more focused on acting. But later, in December 2013, she said it is not possible. In February 2013, Agron hosted her very first You, Me and Charlie concert in Los Angeles, where she performed Fleetwood Mac's "Dreams" and Tina Turner's "What's Love Got to Do with It" featuring the band A House For Lions. In November 2014, Agron, among many other international artists, was featured in United Nations Children's Fund (UNICEF)'s charity single "Imagine" which was originally performed by John Lennon.
In July, 2015, Agron performed The Star-Spangled Banner for the 239th Anniversary of Independence at the Winfield House in London.
In 2010, Agron directed the music video for "Body" by Thao & The Get Down Stay Down. On November 25, 2013, the music video of "Just Another Girl" by The Killers was released, in which Agron portrays the lead singer. Agron starred as a scorned bride in Sam Smith's "I'm Not the Only One" music video which was released on August 1, 2014. In 2014, Agron directed the music video for "Till Sunrise" by Goldroom. Her brother, Jason, and actress Gabby Haugh star as a romantic couple.
In 2009, Agron wrote, starred in, directed, and executive-produced an unreleased short comedy film called A Fuchsia Elephant. The plot revolves around Agron's character. On the day before her eighteenth birthday, Charlotte Hill makes a decision to change. Not wanting to follow in the footsteps of her alcoholic mother, she enlists a sober partner named Michael (Dave Franco) to help guide her. It was shot during the Glee hiatus in the summer of 2009. That same year, Agron hosted a mini music festival for 826LA called Chickens in Love. Agron hosted the GLAAD Media Awards on June 2, 2012, in San Francisco. In 2012 and 2013, Agron appeared in the "Play As You Are" Nintendo campaign, ads for Art Academy: Lessons for Everyone!, and in spots for the puzzle-solving adventure Professor Layton and the Miracle Mask.
Agron spoke at the 18th San Francisco Power of Choice Luncheon to celebrate the 40th Anniversary of Roe V. Wade – 40 years of Choice! on March 7, 2013, in San Francisco, and attended The Hollywood Reporter and Jimmy Choo 2nd Annual 25 Most Powerful Stylists Luncheon on March 13, 2013 in West Hollywood. For the February 2014 issue of the Galore magazine, Dianna worked as the photographer. Her brother, Jason Agron, also helped for the shoot. After directing Thao & The Get Down Stay Down's music video "Body", and her independent unreleased film A Fuchsia Elephant, Agron stated that she would like to continue directing different projects. In May 2015, she directed a video for Tory Burch's Paris collection that will come out later in the year and she was later selected by Burch to represent the brand at the 2015 Met Gala.
Agron underwent nose surgery twice to repair her deviated septum, once the result of a blow to the nose when she was fourteen in a party, and once in an accident while on tour for Glee. In late 2015, she became engaged to Winston Marshall, from the band Mumford & Sons. They were married on October 15, 2016, in Morocco.
Agron has supported PETA and LGBT rights. Using her Tumblr account as a starting point, Agron released her website You, Me and Charlie on December 12, 2011. Along with help from several other contributors, she writes and collects posts, which subjects vary from music, art, fashion, and daily inspiration.
The site serves as inspiration for many young artists. Vanity Fair has complimented the site, stating that the site is "full of sunshine, optimism, and pretty people." Agron hosted the GLAAD Media Awards on June 2, 2012 in San Francisco. Her co-stars of Glee, Naya Rivera and Cory Monteith hosted them on March 24, 2012 in New York City. Following Rivera's tradition of auctioning off kisses to an audience member, she raised $5,500 for the campaign. Agron worked with The Trevor Project in 2012 to raise money in honor of her birthday. Also in 2012, Agron visited the Kampong Cham Center, where she met children and teenage residents. On April 20, 2013, Agron's fans honored her by raising $10,200 for her birthday, benefiting the Somaly Mam Foundation in effort to fight human trafficking.
Agron donated possessions to the Vietnam Veterans of America in Los Angeles during August 2013. Agron also supports the initiative between Camp Wonder and Cetaphil, which is about children with chronic and life-threatening skin diseases to enjoy being a kid. On February 22, 2014, Agron participated along with other Glee stars in the Young Storytellers Foundation biggest show, Glee Big Show, which featured live performances of five scripts written by 5th Grade Young Storytellers to support art programs in public schools.
In June 2014, Agron joined with other celebrities and the Big Slick Foundation weekend charity event to help raise funds for Children's Mercy Hospital of Kansas City, Missouri. Among the events Agron was involved in was a celebrity softball game, a private get-together for patients and celebrities, a bowling tournament, and a celebrity party and auction.
In December 2014, Agron provided services and live entertainment to United States troops and their families as part of the United Service Organizations tour at Bagram air field, Afghanistan. Later that month, she attended to the 10th anniversary gala of a ASmallWorld and sold a kiss for more than $20,000. She donated the money to the War Child charity.
In May 2016, she traveled with the UN to visit resettled Syrian refugees in Europe. She has stated, in response to questions about her intent, that she "came here to help tell the stories of specific individuals because when you meet one of the 60 million forced to flee their home, and you put a name and a face to a number, the global refugee crisis becomes impossible to ignore."