Scarlett Johansson was born in New York City. Her mother, Melanie Sloan, is from a Jewish family from the Bronx, and her father, Karsten Johansson, is a Danish-born architect, from Copenhagen. She has a sister, Vanessa Johansson, who is also an actress, a brother, Adrian, a twin brother, Hunter Johansson, born three minutes after her, and a paternal half-brother, Christian. Her grandfather was writer Ejner Johansson.

Johansson began acting during childhood, after her mother started taking her to auditions. She made her professional acting debut at the age of eight in the off-Broadway production of "Sophistry" with Ethan Hawke, at New York's Playwrights Horizons. She would audition for commercials but took rejection so hard her mother began limiting her to film tryouts. She made her film debut at the age of nine, as John Ritter's character's daughter in the fantasy comedy North (1994). Following minor roles in Just Cause (1995), as the daughter of Sean Connery and Kate Capshaw's character, and If Lucy Fell (1996), she played the role of Amanda in Manny & Lo (1996). Her performance in Manny & Lo garnered a nomination for the Independent Spirit Award for Best Lead Female, and positive reviews, one noting, "[the film] grows on you, largely because of the charm of ... Scarlett Johansson", while San Francisco Chronicle critic Mick LaSalle commentated on her "peaceful aura", and wrote, "If she can get through puberty with that aura undisturbed, she could become an important actress."

After appearing in minor roles in Fall (1997) and Home Alone 3 (1997), Johansson garnered widely spread attention for her performance in The Horse Whisperer (1998), directed by Robert Redford, where she played Grace MacLean, a teenager traumatized by a riding accident. She received a nomination for the Chicago Film Critics Association Award for Most Promising Actress for the film. In 1999, she appeared in My Brother the Pig (1999) and in the music video for Mandy Moore's single, "Candy". Although the film was not a box office success, she received praise for her breakout role in Ghost World (2001), credited with "sensitivity and talent [that] belie her age". She was also featured in the Coen Brothers' dark drama The Man Who Wasn't There (2001), opposite Billy Bob Thornton and Frances McDormand. She appeared in the horror comedy Eight Legged Freaks (2002) with David Arquette and Kari Wuhrer.