Johansson was born in New York City. Her father, Karsten Johansson, was born in Denmark and her paternal grandfather, Ejner Johansson, was a screenwriter and director. Her mother, Melanie Sloan, comes from a Bronx-bred Jewish American family, and met Karsten Johansson while living in Denmark with Scarlett Johansson's maternal grandmother, Dorothy, a former bookkeeper and schoolteacher. Johansson has an older sister, Vanessa, who is also an actress, an older brother, Adrian, a twin brother Hunter, also an actor, and a half-brother, Christian.

Johansson began her theater training by attending and graduating from Professional Children's School in Manhattan in 2002, a school renowned for its theater and acting training to young, hopeful actors and actresses.

Johansson's acting career debuted in Hollywood and garnered praise and widespread attention with her role in The Horse Whisperer. Following the critical success of the 1998 picture, she followed with major roles as Rebecca in Ghost World, Charlotte in Lost in Translation, Griet in Girl with a Pearl Earring, Francesca in The Perfect Score and Nola in Match Point. Most of her performances received positive critical notice.

In 2003, she was nominated for two best actress awards at the Golden Globes, one for drama (Girl with a Pearl Earring) and one for comedy (Lost in Translation). She was also nominated for best actress for both films at the BAFTAs, and won best actress for Lost in Translation.

She was invited to join the Academy of Motion Picture Arts and Sciences in June 2004. In the same year, she starred in A Love Song for Bobby Long, a film that, despite being widely ignored by the movie-going public (grossing only $964,308 worldwide), earned her a third Golden Globe Award nomination.

Johansson was involved for a short time in the film Mission: Impossible III but did not officially join the cast because of scheduling conflicts, although a falling out with Tom Cruise had been both widely reported but quickly denied. She was replaced by Keri Russell.

In July 2005, Johansson starred with Ewan McGregor in the Michael Bay-directed The Island, making her debut as a female lead in a mainstream action film. She drew attention to both the film and herself when she proposed that she'd wanted to film the sex scene in the film topless, but director Michael Bay disapproved, wanting to keep the film at a PG-13 rating. Though produced with high expectations, when the movie opened to weak reviews and an even weaker box office, the producers of the film accused Johansson of failing to connect with and attract a mainstream audience.

Her film Match Point, directed by Woody Allen, opened in December of 2005. Johansson received her fourth Golden Globe nomination for Best Supporting Actress but lost to Rachel Weisz. Johansson's next film, Scoop, another collaboration with director Woody Allen, was released on July 28, 2006.

In July of 2006, Johansson was cast opposite Natalie Portman and Eric Bana in The Other Boleyn Girl, playing Mary Boleyn, the sister of Portman's character. Filming will begin in London in October 2006 for a 2007 release. The same month, Johansson was reported to be in negotiations to play Lucy Ewing in the film version of the television soap opera, Dallas; however, Johansson's publicist has denied the reports and noted that she is "not involved" in the project. She has also been a recurring cast member of Seth Green's stop motion animation series, Robot Chicken.

On August 14, 2006, news emerged that Johansson may replace Teresa Palmer as Millie in Doug Liman's upcoming sci-fi thriller Jumper.

Johansson played a primary role in the music video for lengendary song writer and performer Bob Dylan for "When the Deal Goes Down...".

Johansson endorsed the Calvin Klein perfume "Moment" and was featured in several commercials and printed advertisements for the product. Further establishing her position in Hollywood, she became the face and spokesperson for the French luxury brand Louis Vuitton in early 2005 and in January 2006 was named the spokesperson of L'Oreal.

In early 2006, Johansson appeared on the controversial cover of the February 2006 issue of Vanity Fair in nude with other Hollywood it girl Keira Knightley and world-renowned fashion designer Tom Ford. In March of 2006, she topped the U.S. edition of FHM's poll of the sexiest women alive (in the UK edition Johansson was third). In May of 2006, Maxim named Johansson #6 in their Hot 100 issue, and in July of 2006, Reebok signed a deal with Johansson to co-create "Scarlett "Hearts" Rbk", athletic footwear scheduled for a debut in the spring of 2007. Johansson will also be featured in Reebok's global women's advertising campaign, also in the spring of 2007. The company's press releases described Johansson as a "world renowned style icon" and an "inspiration for today's young women".

Johansson is a Democrat and campaigned for John Kerry in the 2004 Presidential Election. Johansson has also taken part in an anti-poverty campaign which was organized by U2 lead singer, Bono.

Johansson is reportedly dating actor Josh Hartnett, but had previously stated that she has a connection to older men and could not see herself dating anyone under the age of thirty. She has also noted that she does not discuss "any part" of her personal life with the press, specifying that "it's nice to have everybody not know your business."

Johansson has claimed to be addicted to cheese, saying "My greatest vice is cheese. Nothing else reigns over my life."