Cavill, 27, proposed to Ellen Whitaker, who's training to make the 2012 British Olympic team, while they were on a trip to Hollywood.
"I couldn't believe it when he asked me to marry him," she told the newspaper. "I thought we were there to celebrate his birthday. It was such a surprise and I am so happy."
Cavill most recently appeared in Showtime's The Tudors and will star in Superman: Man of Steel slated for release in December 2012.