The world number five will feature in a series of consumer brand campaigns specifically designed to engage Sony Ericsson's core target audiences and to make use of Sharapova away from the tennis court.
The 20-year-old will also be working with the company's design team on a range of products and accessories.
The off-court agreement supports Sony Ericsson's six-year $88m global title sponsorship of the Women's Tennis Association (WTA) Tour, which was signed in January 2005.
The deal coincided with the start of the Australian Open in Melbourne yesterday, where Sharapova has reached the second round after beating Jelena Kostanic Tosic.
Dee Dutta, corporate vice-president and head of marketing at Sony Ericsson, said:
"Now in our seventh year as a company, the brand has evolved significantly and securing a global brand ambassador is a natural progression to take our band to the next level in an increasingly competitive market place.
"Maria's iconic status, determination, dynamism, success and charm match strongly with the Sony Ericsson brand, which prides itself on innovative and cool design with substance."
Sharapova said: "Even though most people know me as a tennis player, I have so many passions beyond the sport like fashion, music, film and design; which Sony Ericsson and I are going to be exploring together through our partnership."
Sony Ericsson used tennis players Ana Ivanovic and Daniela Hantuchova in a 2006 TV ad to back the launch of its K800 and K790 Cyber-Shot camera phones.