Hathaway, 30, was the favorite to win this year's Academy Award for Best Supporting Actress. She used a strict diet of dried oatmeal paste to shed 25 pounds (11 kg), hacked off her long hair and spent six months perfecting the task of crying and singing at the same time for her heart-wrenching rendition of "I Dreamed a Dream."
"It came true," Hathaway said upon accepting her gold statue.
During press tours, she frequently spoke of her family connection to Fantine, a starving young mother forced into prostitution.
Hathaway was just 7 years old when she saw her mother, who was understudy for the role during the show's first tour of the United States, play Fantine.
"Here's hoping that some day, in the not too distant future, the misfortunes of Fantine will only be found in stories and never more in real life," Hathaway said.
"Les Miserables" stars, including Hathaway and Best Actor nominee Hugh Jackman, were put through an intense audition and rehearsal process to prepare them to sing live take after take with cameras positioned right in front of their faces.
The tactic paid off. The film was a box office success and the soundtrack hit the top of the album charts in both the United States and the United Kingdom.
Hathaway picked up a Best Actress nominee for her leading role in the 2008 drama "Rachel Getting Married."
Her rivals for this year's Best Supporting Actress prize were Oscar-winners Sally Field and Helen Hunt as well as previous Academy Award nominees Amy Adams and Jacki Weaver.
Hathaway also is know for her roles in "The Princess Diaries," "Brokeback Mountain," "The Devil Wears Prada" and "The Dark Knight Rises."