The 24-year-old, who is famed for her eccentric outfits and risque videos, was holidaying with the club promoter in the Greek island of Crete, when they decided to have the ceremony, reported Daily Mail online.
The popstar and Carl, 29 exchanged handwritten vows and rings during the secret ceremony.
"They exchanged rings in a spiritual service and drank shots before sitting down to a lovely private dinner at a tiny restaurant. They wanted to show that they are committed to each other and want to spend the rest of their lives together," said a source close to the couple.
Gaga is now planning a big wedding later on with all her friends and family.
"They are still planning to marry, but that will come later when she has the time to plan a big Italian-style wedding," added the source.