Bridget Marquardt, born Bridget Christina Sandmeier, was born in Tillamook, Oregon. Shortly after her birth, Marquardt's mother moved the family back to California, where Marquardt was raised. Her parents divorced when Marquardt was in the fifth grade. Her mother remarried, and Marquardt and her younger brother Edward moved to their stepfather's ranch, where they later gained a half-sister, Anastasia. Marquardt attended Galt High School for her freshman and sophomore years and then transferred to Lodi High School, from which she graduated in 1990.
Marquardt graduated from San Joaquin Delta College with an associate degree. She matriculated to California State University, Sacramento and graduated in 1998 with a B.A. in communications and an emphasis on public relations. In 2001, she earned her Master's Degree in Communications from the University of the Pacific in Stockton, California.
She later took a graduate level course in broadcast journalism through UCLA Extension, which was depicted on the first season of The Girls Next Door, most notably when she had to be absent from her first Playboy shoot in order to take her final exam.
On the advice of friends who suggested she pose for Playboy magazine, Marquardt sent a letter to Playboy, inquiring how to become a Playmate, before enrolling at San Joaquin Delta College. In 1998, aged 25, she entered Playboy's Millennium Playmate search. In 2001, Marquardt moved to Los Angeles, California and did local modeling jobs and small acting roles. After unsuccessfully testing twice for Playboy, she was invited to the Playboy Mansion and soon became a regular there. In October 2002, after more than a year of visiting the Mansion, she was invited to move in and become one of Hefner's girlfriends.
Marquardt is featured on the E! TV show The Girls Next Door, and has appeared with Holly Madison and Kendra Wilkinson in three cover pictorials in Playboy magazine, the November 2005, September 2006 and March 2008 issues. She has appeared in several films, including the horror/comedy Kottentail in which she portrays a scientist doing genetic research on rabbits. She appeared in an episode of Curb Your Enthusiasm as herself along with Madison and Hefner in 2005. She also appeared as herself along with Madison, Wilkinson and Hefner in the Entourage episode "Aquamansion". The episode's final act took place at the Playboy Mansion. She appeared in The House Bunny with her fellow models and Hefner alongside Anna Faris.
Marquardt appeared in a 2002 episode of The Man Show as one of Hefner's playmates in the video game Playboy: The Mansion, which was released in January 2005, as well as in an episode of Celebrity Paranormal Project which aired on November 19, 2006. She took an online paranormal course because of her interest in paranormal activity. On June 1, 2007, she started her Bridget & Wednesday Friday Show on Sirius Radio's Playboy station. In August of that year, she, Madison and Wilkinson appeared in the music video for Nickelback song "Rockstar". Later that October, Marquardt appeared as a contestant on the Fox Reality cable show The Search for the Next Elvira. She was one of the final six out of 20 contestants.
In 2008, Marquardt appeared on an episode of NBC's Last Comic Standing along with Wilkinson and Madison in an episode in which the girls were told funny "bedtime stories" by the competing comics. In June of that year, Marquardt landed her own TV series, Bridget's Sexiest Beaches, which aired on the Travel Channel. Marquardt and the rest of the Girls Next Door appeared in a July 1, 2008 episode of NBC’s Celebrity Family Feud.
February 2009 was Marquardt's final appearance in Playboy, in a nude photo spread shot with Madison and Wilkinson that was touted as a farewell to the Girls Next Door. After leaving Playboy, she hosted Bridget's Sexiest Beaches, a TV series on Travel Channel, which debuted on March 12, 2009, but ended after one season.
In April 2010, Marquardt announced plans for her own reality show. The pilot was to begin shooting in April and would cover her life after leaving the Playboy Mansion, and on her current relationships. In March 2011, she announced via Twitter that E! had decided to not pick up her reality show but stated that she was looking forward to other opportunities.
In 2012, she worked as a contributor to Yahoo's Animal Nation series, writing articles and shooting related short documentary pieces.
In the September 17, 2007 issue of Star magazine, Marquardt stated that she was married, but separated and had been living in the Playboy mansion since October 2002. According to the interview, her husband supported her move to Los Angeles, that they remained friends, and that they were in the process of divorcing.
On September 25, 2008, Bridget told E! News, "I married my best friend when I was 23, but when I realized I wanted to move to LA to follow my dreams, we separated and eventually divorced." In a December 2008 interview, Marquardt stated that she was single, and in early January 2009, it was reported that Marquardt had moved out of the Playboy Mansion to "become her own person."
In late 2008, Marquardt began dating director Nicholas Carpenter, son of original Mercury astronaut Scott Carpenter. They live together in a house Marquardt purchased in Sherman Oaks. The pair became engaged in the fall of 2015. As seen on various episodes of The Girls Next Door, Marquardt has a Pekingese dog named Wednesday, or "Winnie", and a black Persian cat named Gizmo. Gizmo died June 2015.