Emma Watson was born in Paris, France, daughter of Jacqueline Luesby and Chris Watson, English lawyers. Watson has one French grandmother, and lived in Paris until the age of five, before she moved with her mother and younger brother Alex to Oxford, England, following her parents' divorce.

From six, Watson expressed a desire to become an actress. By 10, she had starred in school plays, including Arthur: The Young Years and The Happy Prince. She had never acted professionally before the Harry Potter series. "I had no idea of the scale of the film [series]", she said in a 2007 interview with Parade magazine; "[if I had] I would have been completely overwhelmed".

In 1999, casting began for Harry Potter and the Philosopher's Stone (known as Harry Potter and the Sorcerer's Stone in the United States), the film adaptation of British author J. K. Rowling's bestselling novel.

Of importance to the casting directors were the lead role of Harry Potter and the two supporting roles of Hermione Granger and Ron Weasley, Harry's two friends. Casting agents found Watson through her Oxford theatre teacher, and producers were impressed by her confidence.

After eight auditions, producer David Heyman told Watson and fellow applicants Daniel Radcliffe and Rupert Grint that they had been cast as Hermione Granger, Harry Potter and Ron Weasley. Rowling was said to support Watson from her first screen test.

Watson's debut as Hermione came in 2001 with Harry Potter and the Philosopher's Stone. The film broke records for opening-day sales and opening weekend takings and was the highest-grossing film of 2001. Critics praised the performances of the three leads, often singling out Watson for particular acclaim.

The Daily Telegraph called her performance "admirable", and IGN said she "stole the show". Watson was nominated for five awards for her performance in Philosopher's Stone, winning the Young Artist Award for Leading Young Actress.

A year later, Watson again starred as Hermione in Harry Potter and the Chamber of Secrets, the second instalment of the series. Though the film received mixed reviews because of its pace and direction, critics were positive about the performances. The Los Angeles Times said Watson and her peers had matured between films, while The Times criticised director Chris Columbus for "under-employing" Watson's hugely popular character.

Watson received an Otto Award from the German magazine Die Welt for her performance. In 2004, Harry Potter and the Prisoner of Azkaban was released. Watson was appreciative of the more assertive role Hermione played, calling her character "charismatic" and "a fantastic role to play". Although critics turned away from Radcliffe's acting talent, labelling him wooden, Watson continued to be praised; The New York Times lauded her performance, saying "Luckily Mr. Radcliffe's blandness is offset by Ms. Watson's spiky impatience.

Harry may show off his expanding wizardly skills ... but Hermione ... earns the loudest applause with a decidedly unmagical punch to Draco Malfoy's deserving nose". Although Prisoner of Azkaban remains the lowest-grossing Harry Potter film as of January 2008, Watson's personal performance won her two Otto Awards and the Child Performance of the Year award from Total Film.

With Harry Potter and the Goblet of Fire (2005), both Watson and the Harry Potter film series reached new milestones. The film set records for a Harry Potter opening weekend, a non-May opening weekend in the US, and an opening weekend in the UK.

Critics praised the increasing maturity of Watson and her teenage co-stars; the New York Times called her performance "touchingly earnest". For Watson, much of the humour of the film sprang from the tension among the three lead characters as they matured. She said, "I loved all the arguing ... I think it's much more realistic that they would argue and that there would be problems."

Nominated for three awards for Goblet of Fire, Watson won a bronze Otto Award. Later that year, Watson became the youngest person to appear on the cover of Teen Vogue. 2006 found Watson playing Hermione in The Queen's Handbag, a special mini-episode of Harry Potter in celebration of Queen Elizabeth II's 80th birthday.

The fifth film in the Harry Potter franchise, 2007's Harry Potter and the Order of the Phoenix, was a financial success, setting a record worldwide, opening-weekend gross of $333 million. Watson won the inaugural National Movie Award for Best Female Performance.

As the fame of the actress and the series continued, Watson and fellow Harry Potter co-stars Daniel Radcliffe and Rupert Grint left imprints of their hands, feet, and wands in front of Grauman's Chinese Theater in Hollywood on 9 July 2007.