Miss Roy took top prize in the 84th annual US National Spelling Bee after she saw off her competitors over 20 rounds of on-the-spot spelling at the final in Oxon Hill, Maryland.
After winning, the teenager, who was competing in her third championships, was shaking with excitement.
"My heart started pounding, I guess. I couldn't believe it," Miss Roy told broadcaster ESPN, immediately after receiving her trophy.
The finals have been screened live on US television since 2006 and drew and audience of over one million last year.
The winning word, cymotrichous, is an adjective relating to having wavy hair. Miss Roy, who also speaks fluent Bengali, said she knew the word immediately.
"I just wanted to spell it right," she said. "I really didn't want to get it wrong."
Besides the trophy, the newly-crowned champion speller took home a $30,000 cash prize, a $2,500 US savings bond, a complete reference library, a $5,000 scholarship, $2,600 in reference works and other prizes. -03 Jun 2011