Garner was born in Houston, Texas, to Patricia Ann English, a teacher, and William Jack Garner, a chemical engineer; she is the middle child between two sisters, Melissa Garner Wiley and Susannah Garner Carpenter. When she was four years old, her father's job with Union Carbide forced the family to relocate to Charleston, West Virginia, where Garner resided until her college years. In 1990, Garner graduated from George Washington High School in Charleston, where she played the saxophone [1]. She also studied ballet for nine years before enrolling at Denison University to study chemical engineering. Upon realizing that she enjoyed stage acting more than science, Garner changed her major to drama. Garner graduated from Denison in 1994, and planned to continue her drama education at Yale University. However, keen for experience, she visited a friend in New York City in 1995 and decided to take her chances in theatre.

In New York City, Garner earned $150 a week as an understudy in a play. She was then cast in her first television role, a part in the made-for-television movie, Zoya, based on the Danielle Steele novel. Her next acting jobs were in two short-lived television series, Significant Others and Time of Your Life, as well as in two Hallmark Hall of Fame movies, including the 1997 film, Rose Hill, based on the best selling book For The Roses by Julie Garwood. In 1996, she appeared on an episode of the NBC drama Law & Order. She played a college student who engaged in an affair with Detective Rey Curtis. Subsequently, Garner moved to Los Angeles, California, and got a job as a hostess at a restaurant before being cast as Hannah Bibb on the WB series, Felicity. On the set, she met her future husband, Scott Foley. Garner played his character's girlfriend. In 2000, Garner appeared in the comedy Dude, Where's My Car?, playing Ashton Kutcher's girlfriend. In 2001, she appeared as a nurse in the big-budget version of Pearl Harbor, co-starring Ben Affleck and Kate Beckinsale.

Later in 2001, J. J. Abrams, who produced Felicity, approached Garner about starring in a new show he was working on for ABC. Garner auditioned and was cast in the role of Sydney Bristow in the spy drama Alias. The series became a success and Garner won the award for "Best Actress in a Television Series - Drama" at the January 2002 Golden Globes. Alias had just begun a few months beforehand, and Garner won the award with only half the season's episodes aired. The series had a successful run since, and concluded in May 2006 during its fifth season. Garner's salary for the show began at $45,000 an episode, and had since risen to $150,000 per episode. During the show's run, Garner received four consecutive Golden Globe nominations for her lead performance. She has also received four consecutive Emmy nominations for "Outstanding Lead Actress in a Drama Series". Garner won the "Actor Award" from the Screen Actors Guild in 2005. The category had only five nominees and is composed of all actresses in any dramatic roles, both lead and supporting. In March 2005, Garner directed "In Dreams," an Alias episode which aired in May. Garner has been receiving "producer/director" credit for the series in it's fifth and final season.

After the initial success of Alias, Garner returned to her film career with a small role in the Steven Spielberg film Catch Me If You Can, and starred alongside Ben Affleck as Elektra Natchios in the action movie Daredevil, an adaptation of the comic book. She reprised her role as "Elektra" in the 2005 spin-off to Daredevil, entitled Elektra. Garner showed her comedic side in the romantic comedy 13 Going on 30, which was a financial success and established her as a leading feature film actress. Garner is known for performing her own stunts, and in January 2005 was forced to bow out of some publicity duties for Elektra, due to what was first thought to have been a viral infection but was revealed to be the effects of nerve damage to her back, caused by a stunt during the filming of Alias.

Garner entered the Forbes "Power 100" list of celebrities in 2005. She ranked as the 5th best paid actress in Hollywood, accumulating an estimated US $14 million over the year 2004/05 [2]. She came 8th behind Cameron Diaz in the power rankings. During the 2006 Academy Awards ceremony, Garner stumbled on her flowing dress (designed by Michael Kors) as she came onto the stage to present the award for Sound Editing. She did not fall, but lost her balance, and jokingly commented, "I do my own stunts!" Garner's next film will be the romantic comedy Catch and Release. She also did voice work for the 2006 version of Charlotte's Web. Garner has formed a production company named Vandalia Films, which will produce its first film in 2007. She will produce the company's upcoming films.

On October 19, 2000, Garner married actor Scott Foley, her Felicity co-star. The two were officially divorced in March 2004. Garner then dated her Alias co-star Michael Vartan until mid-2004, when she began dating her Daredevil co-star Ben Affleck.

On June 29, 2005, Garner and Affleck were married in a surprise ceremony at the Parrot Cay resort on the Turks and Caicos Islands. Around this period, Garner was pregnant with the couple's first child. Officiating at the ceremony was her Alias co-star Victor Garber. Her pregnancy was incorporated into the plot of Alias, [3] with the season's episode order cut by a few episodes in order to let Garner go on maternity leave. On December 1, 2005, she gave birth to their daughter, Violet Anne Affleck.

Garner enjoys cooking, gardening, hiking and kickboxing (a hobby inspired by her Alias character).