Alexandra Breckenridge was born on May 15, 1982, in Bridgeport, Connecticut. She lived in Darien, Connecticut, until the age of 10, when she and her mother moved to California. After a year of moving around, they settled in Mill Valley. Breckenridge developed an interest in acting, photography, and singing at the age of 13.

When she was 15, she and her mother moved back to Los Angeles so she could pursue an acting career. At 19, she worked as a delivery driver for Big Wangs in Hollywood. Her mother, who was 19 when Alexandra was born, attended college and worked as a house cleaner. Her father worked as a director of operations in the engineering department at Foxwoods Casino.

Breckenridge began her acting career with guest roles in various television shows, including "Freaks and Geeks," "Buffy the Vampire Slayer," "Charmed," "CSI: Crime Scene Investigation," "Dawson's Creek," "JAG," "Medium," "Psych," and "Undeclared." She also appeared as Francise in three episodes of "Opposite Sex."

In 2002, Breckenridge played Janie Shepherd, the older sister of Frankie Muniz’s character, in the film "Big Fat Liar." She gained recognition for her voice work on the animated television series "Family Guy," where she frequently did celebrity impressions such as Sarah Jessica Parker and Renée Zellweger. Breckenridge also appeared in Seth MacFarlane's web series "Cavalcade of Cartoon Comedy" and guest-starred in an episode of "American Dad!" titled "With Friends Like Steve's."

In 2006, Breckenridge starred as Monique in the film "She's the Man." She had a recurring role in the FX drama series "Dirt" (2007-2008) as Willa McPherson, a young writer. In 2009, she co-starred in the independent film "The Bridge to Nowhere," directed by Blair Underwood.

In 2011, Breckenridge gained wider recognition for her role as young Moira O'Hara in the first season of FX's "American Horror Story." She returned for the third season, "Coven," as Kaylee, a young witch skilled in pyrokinesis. She also had a recurring role as Katerina Pelham in the fourth season of HBO's "True Blood."

From 2015 to 2016, Breckenridge portrayed Jessie Anderson in seasons five and six of AMC’s "The Walking Dead," a character from the comic book series. In 2015, she co-starred in the psychological thriller "Dark," produced by Joe Dante and directed by Nick Basile. In 2017, she played Sophie, Kevin's ex-wife and Kate's childhood friend, in the NBC drama series "This Is Us." Breckenridge was promoted to a series regular for the second season and continued to appear in subsequent seasons, including the final sixth season.

Since 2019, Breckenridge has starred as Melinda "Mel" Monroe in the Netflix series "Virgin River," where she plays a nurse-midwife who relocates to a small town in northern California following a personal tragedy. The series has been renewed for fourth and fifth seasons by Netflix as of September 2021.

Breckenridge married guitarist Casey Hooper in September 2015. They have two children: a son born in September 2016 and a daughter born in December 2017. The family resides in Georgia.

Breckenridge is the niece of actor Michael Weatherly. She has several tattoos that are covered by makeup for her on-screen roles but are visible during photo shoots.