Alba was born in Pomona, California, to Catherine Louisa (née Jensen) and Mark David Alba. Her mother has Danish, Welsh, German, English, and French ancestry, while her paternal grandparents, who were born in California, were both the children of Mexican immigrants. She has a younger brother, Joshua. Her third cousin, once removed, is writer Gustavo Arellano. Her father's Air Force career took the family to Biloxi, Mississippi, and Del Rio, Texas, before settling back in Claremont, California, when she was nine years old. Alba has described her family as being a "very conservative family – a traditional, Catholic, Latin American family" and herself as very liberal; she says she had identified herself as a "feminist" as early as age five.
Alba's early life was marked by a multitude of physical maladies. During childhood, she suffered from partially collapsed lungs twice, had pneumonia four to five times a year, as well as a ruptured appendix and a tonsillar cyst. Alba became isolated from other children at school, because she was in the hospital so often due to her illnesses that no one knew her well enough to befriend her. Alba has also had asthma since she was a child. Alba has said that her family's frequent moving also contributed to her isolation from her peers. She has acknowledged that she suffered from obsessive–compulsive disorder during her childhood. Alba graduated from Claremont High School at age 16, and she subsequently attended the Atlantic Theater Company.
Alba expressed an interest in acting from the age of five. In 1992, the 11-year-old Alba persuaded her mother to take her to an acting competition in Beverly Hills, whose grand prize was free acting classes. Alba won the grand prize, and took her first acting lessons. An agent signed Alba nine months later. Her first appearance on film was a small role in the 1994 feature Camp Nowhere as Gail. She was originally hired for two weeks but her role turned into a two-month job when one of the prominent actresses dropped out.
Alba appeared in two national television commercials for Nintendo and J. C. Penney as a child. She was later featured in several independent films. She branched out into television in 1994 with a recurring role as the vain Jessica in three episodes of the Nickelodeon comedy series The Secret World of Alex Mack. She then performed the role of Maya in the first two seasons of the television series Flipper. Under the tutelage of her lifeguard mother, Alba learned to swim before she could walk, and she was a PADI-certified scuba diver, skills which were put to use on the show, which was filmed in Australia.
In 1998, she appeared as Melissa Hauer in a first-season episode of the Steven Bochco crime-drama Brooklyn South, as Leanne in two episodes of Beverly Hills, 90210, and as Layla in an episode of The Love Boat: The Next Wave. In 1999, she appeared in the Randy Quaid comedy feature P.U.N.K.S.. After Alba graduated from high school, she studied acting with William H. Macy and his wife, Felicity Huffman, at the Atlantic Theater Company, which was developed by Macy and Pulitzer Prize-winning playwright and film director, David Mamet. Alba rose to greater prominence in Hollywood in 1999 after appearing as a member of a snobby high school clique in the Drew Barrymore romantic comedy Never Been Kissed, and as the female lead in the 1999 comedy-horror film Idle Hands, opposite Devon Sawa.
Her big break came when writer/director James Cameron picked Alba from a pool of 1,200 candidates for the role of the genetically engineered super-soldier, Max Guevara, on the Fox sci-fi television series Dark Angel. Co-created by Cameron, the series starred Alba, and ran for two seasons until 2002, earning her critical acclaim as well as a Golden Globe nomination. Alba later admitted to suffering from anorexia while in preparation for Dark Angel.
Alba has been well received in popular culture. She received the Teen Choice Award for "Choice Actress" and Saturn Award for Best Actress for her role in Dark Angel. In 2006, Alba received an MTV Movie Award for "Sexiest Performance" for Sin City. Her acting has also drawn criticism, however, as she was nominated for the Razzie Award for Worst Actress in 2005 for her performances in Fantastic Four and Into the Blue. She was nominated for the same award for 2007's Awake, Good Luck Chuck, and Fantastic Four: Rise of the Silver Surfer.
Alba's film roles have included an aspiring dancer-choreographer in Honey, exotic dancer Nancy Callahan in Sin City, and as the Marvel Comics character Sue Storm, the Invisible Woman, in Fantastic Four and its sequel. She also starred in Into the Blue (2005) and Good Luck Chuck (2007). Alba hosted the 2006 MTV Movie Awards and performed sketches spoofing the movies King Kong, Mission: Impossible III, and The Da Vinci Code. In February 2008, she hosted the Academy of Motion Picture Arts and Sciences' Science and Technical Awards. Alba has been represented by talent agents Patrick Whitesell and Brad Cafarelli.
In 2008, Alba made her acting transition to the horror-film genre in The Eye, a remake of the Hong Kong original. The film was released on February 1, 2008. Though the film was not well received by critics, Alba's performance itself received mixed reviews. Alba won a Teen Choice for Choice Movie Actress: Horror/Thriller and a Razzie Award for Worst Actress-nomination. Also in 2008, Alba starred alongside Mike Myers and Justin Timberlake in "box office bomb" The Love Guru. Alba was nominated for a Razzie Award for Worst Actress.
In late 2008, Alba signed on to star as the lead role in An Invisible Sign of My Own. The movie finished filming in November 2008. It premiered at the Hamptons International Film Festival and was released to theaters in May 2011.
In 2010, Alba starred in five films. She played Joyce Lakeland, a prostitute in The Killer Inside Me, film adaption of the book of the same name which co-starred Kate Hudson and Casey Affleck. The film premiered at the Sundance Film Festival. Her second film of the year was the hit romantic comedy Valentine's Day, directed by Garry Marshall. She portrayed Ashton Kutcher's girlfriend, Morley Clarkson, in the ensemble film that included Julia Roberts, Anne Hathaway, Jessica Biel, Bradley Cooper, and Jennifer Garner, among others. Later that year, she appeared in the action film Machete, in An Invisible Sign of My Own and in Little Fockers, reuniting with Robert De Niro who was also in Machete.
In 2011, Alba appeared in the film Spy Kids: All the Time in the World.
In January 2012, Alba and business partner Chris Gavigan launched The Honest Company, a collection of toxin-free household goods, diapers, and body care products. The company is currently valued at $1 billion. In March 2012, Alba announced that she will be releasing a book, The Honest Life, based on her experiences creating a natural, non-toxic life for her family. The book was published in early 2013 by Rodale.
Her 2013 projects include comedy A.C.O.D. and animated film Escape from Planet Earth. Alba reprised her roles, Santana in Machete's sequel Machete Kills, and Nancy Callahan in Sin City: A Dame to Kill For, the sequel to 2005's Sin City. Filming for the Sin City sequel started in October 2012 and the film was released in August 2014.
In 2001, Alba was ranked No. 1 on Maxim magazine's Hot 100 list. She said that "I have to go to certain lengths to use sexuality to my advantage, while guiding People to thinking the way I want them to." In 2005, Alba was named one of People magazine's 50 Most Beautiful People, and also appeared in the magazine's 100 Most Beautiful list in 2007. In 2002, Alba was voted as the fifth Sexiest Female Star for 2002 in a Hollywood.com poll, No.4 in the Top 10 Sci-Fi Babes, No.6 in FHM's Sexiest Girls for their poll, and ranked at No.12 in Stuff magazine's "102 Sexiest Women in the World" 2002 edition. In 2005, Alba was ranked at No.5 on the Maxim magazine's Hot 100 list.
On the cover of the March 2006 issue, Playboy magazine named Alba among its 25 Sexiest Celebrities, and the Sex Star of the Year. Alba was involved in litigation against Playboy for its use of her image (from a promotional shot for Into the Blue) without her consent, which she contends gave the appearance that she was featured in the issue in a "nude pictorial". However, she later dropped the lawsuit after receiving a personal apology from Playboy owner Hugh Hefner, who agreed to make donations to two charities that Alba has supported.
When reports surfaced that a 21-year-old Chinese girl was seeking plastic surgery to resemble Alba in order to win back an ex-boyfriend, the star spoke out against the perceived need to change one's appearance for love.
In 2006, Alba ranked No.3 on E! Television's 101 Sexiest Celebrity Bodies. In 2006 readers of AskMen.com voted Alba No. 1 on 99 Most Desirable Women, while in 2007, Maxim Magazine placed Alba on the number 2 spot of their "Top 100". Both GQ and In Style had Alba on their June 2008 covers, and in May, after eight million votes, FHM (UK and USA editions) named Alba the winner as "2007's Sexiest Woman in the World". Alba has been regarded as one of the world's most attractive women, being named to Maxim's Hot 100 in 2008. In 2007, Alba was ranked in at No.1 in FHM's Sexiest Girls of 2007 poll, in the magazine's Latvian edition. Alba was ranked No.4 on Empire Magazine's 100 Sexiest Movie Stars in 2007. In 2006 and 2007, Alba was voted No.1 as the most sexy woman in the world by the Norwegian FHM. Alba appeared in the 2009 Campari calendar. Campari printed 9,999 copies of the calendar featuring photos of Alba posing sexually in swimsuits, and high heels. In 2008, Alba was ranked No.34 on Maxim magazine's Hot 100 list, was ranked No.2 on Wizard magazine's "Sexiest Women of TV" list, and was named in GQ Magazine one of the 25 Sexiest Women in film of all time. Alba is the only woman who has made the Maxim Magazine Hot 100 list in all the years it was published; from 2000 to 2014. She appeared on Maxim's 2014 Hot 100 list, finishing 8. She was named one of the "100 Hottest Women of All-Time" by Men's Health. People named her one of 2012 Most Beautiful at Every Age.
Alba fears being typecast as a sex kitten based on the bulk of parts offered to her, commenting, "Somehow, I don't think this is happening to Natalie Portman." In the interview, Alba said she wants to be taken seriously as an actress but believes she needs to do movies that she would otherwise not be interested in to build her career, stating that eventually she hopes to be more selective in her film projects. Alba also maintains a strict no-nudity clause in her contract. She was given the option to appear nude in Sin City by the film's directors, Frank Miller and Robert Rodriguez, but declined the offer, saying, "I don't do nudity. I just don't. Maybe that makes me a bad actress. Maybe I won't get hired in some things. But I have too much anxiety". She remarked of a GQ shoot in which she was scantily clad, "They didn't want me to wear the granny panties, but I said, 'If I'm gonna be topless I need to wear granny panties."
Alba was raised as a Catholic throughout her teenage years, but left the church because she felt she was being judged for her appearance, explaining:
"Older men would hit on me, and my youth pastor said it was because I was wearing provocative clothing, when I wasn't. It just made me feel like if I was in any way desirable to the opposite sex that it was my fault, and it made me ashamed of my body and being a woman".
Alba also had objections to the church's condemnations of premarital sex and homosexuality, and what she saw as a lack of strong female role models in the Bible, explaining "I thought it was a nice guide, but it certainly wasn't how I was going to live my life." Her "religious devotion [began] to wane" at the age of 15 when she guest-starred as a teenager with gonorrhea in the throat in a 1996 episode of the television series Chicago Hope. Her friends at church reacted negatively to her role, making her lose faith in the church. However, she has stated that she still holds her belief in God despite leaving the church.
While filming Dark Angel in January 2000, Alba began a three-year relationship with her co-star Michael Weatherly. Weatherly proposed to Alba on her twentieth birthday, which she accepted. In August 2003, Alba and Weatherly announced that they had ended their relationship. In July 2007, Alba spoke out about the breakup, saying "I don't know [why I got engaged]. I was a virgin. He was 12 years older than me. I thought he knew better. My parents weren't happy. They're really religious. They believe God wouldn't allow the Bible to be written if it wasn't what they are supposed to believe. I'm completely different." Alba had at one time said she envisioned a much older man as her ideal partner, making references to Morgan Freeman, Sean Connery, Robert Redford, and Michael Caine. She said, "I have this thing for older men. They've been around and know so much."
Alba met Cash Warren, son of actor Michael Warren, while filming Fantastic Four in 2004. Alba married Warren in Los Angeles in May 2008. They have two daughters: Honor Marie Warren (born 2008) and Haven Garner Warren (born 2011). The first pictures of Honor Marie appeared in the July 2008 issue of OK! magazine, which reportedly paid $1.5 million. In July 2017, Alba announced she and Warren are expecting their third child.
In 2014, Alba appeared in Henry Louis Gates's genealogy series Finding Your Roots, where her lineage was traced back to the ancient Maya civilization. The show's research indicated that the surname Alba did not come from a Spanish man, since her father's direct paternal line (Y-DNA) was Haplogroup Q-L54, Indigenous in origin. Her father's matrilineal line (mtDNA) showed Sephardi Jewish roots, and DNA testing revealed that lawyer Alan Dershowitz is a genetic relative of hers. Jessica's global admixture was 72.7% European, 22.5% East Asian and Native American, 2% Sub-Saharan African, 0.3% Middle Eastern and North African, 0.1% South Asian, and 2.4% "No Match".
Alba's charity work includes participation with Clothes Off Our Back, Habitat for Humanity, National Center for Missing and Exploited Children, Project HOME, RADD, Revlon Run/Walk for Women, SOS Children Villages, Soles4Souls, and Step up. Alba endorsed and supported Democratic presidential hopeful Barack Obama during the 2008 primary season. Alba is an ambassador for the 1Goal movement to provide education to children in Africa. She is also a strong supporter of gay rights and on June 27, 2013, she expressed her delight with the Supreme Court's decision to strike down DOMA on her Twitter account. She tweeted "#equality #love".
Alba posed for a bondage-themed print advertising campaign by Declare Yourself, a campaign encouraging voter registration among youth for the 2008 United States presidential election. The ads photographed by Mark Liddell, which feature Alba wrapped in and gagged with black tape, drew national media attention. Alba said of doing the advertisements that "it didn't freak me out at all." Alba also said, "I think it is important for young people to be aware of the need we have in this country to get them more active politically," and "People respond to things that are shocking."
In June 2009, while filming The Killer Inside Me in Oklahoma City, Alba was involved in a controversy with residents when she pasted posters of sharks around town. Alba said that she was trying to bring attention to the diminishing population of great white sharks. Media outlets speculated that Alba would be pursued and charged with vandalism. On June 16, 2009, Oklahoma City police said that they would not pursue criminal charges against Alba, because none of the property owners wanted to pursue it. Alba apologized in a statement to People magazine and said that she regretted her actions. She later donated an undisclosed amount of money (over $500) to the United Way, whose billboard she had obscured with one of the shark posters.
In 2011, Alba participated in a two-day lobbying effort in Washington D.C. in support of the Safe Chemicals Act, a revision of the Toxic Substances Control Act of 1976.