The Russian world number one defeated the Italian 6-3 6-3 on Court Phillipe Chatrier to become only the sixth female player in the Open era to complete the career Grand Slam.
"It's surreal," she said. "It's the most unique moment I've experienced in my career. I have a tremendous amount of belief and pride in what I do. I love my work."
Sharapova's first Grand Slam was at Wimbledon in 2004 before titles at the US Open in 2006 and the Australian Open in 2008.