In August 2012 Belmonte won two silver medals at the 2012 Summer Olympics in London. The first medal she won was a silver medal in the 200-metre butterfly. Not only was it her first Olympic medal, it was the first medal won by a Spanish-born woman in swimming at an Olympic Games, and it was the first medal for Spain in any sport at the 2012 Summer Olympics. Her second medal was also a silver medal, this time in the 800-metre freestyle behind 15-year-old Katie Ledecky and ahead of world record holder Rebecca Adlington. She became the first Spanish swimmer to win two Olympic medals.