The 17-year-old Russian won this year's Wimbledon Championship and is currently ranked fourth-best womens' tennis player in the world.
The player will feature in TAG Heuer's press campaign "What are you made of", shot by photographer Patrick Demarchelier.
Sharapova said that she saw TAG Heuer as the most "prestigious luxury partner she could dream of".
"[It's] as legendary and glamorous as the individuals and teams with which it is so closely related, and yet at the same time ultra-fashionable and feminine. It's a perfect fit for me, as I love high tech, glamour and winning," she said.
The watchmaker said Sharapova would help promote the Formula 1 and 2000/Aquaracer models, and will be "directly involved" in the development of new products.
Other TAG Hauer representatives include golfer Tiger Woods and Formula 1 driver Kimi Raikkonen.
TAG Heuer is just the latest in a line of brand endorsements that the blonde Sharapova has signed. Other deals inked include sponsorships with Motorola, Canon and Nike, and she has signed a deal with Parlux Fragances to launch her own perfume.
The other Russian tennis favourite Anna Kournikova, who has slipped far down the rankings but her blonde looks regularly score magazine covers, represents Omega watches.
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