"It's such an honour," she said. "I'm a big fan of Pepsi products and Pepsi commercials.
The singer of Oops... I Did It Again and Baby One More Time will appear in Pepsi commercials and the company will sponsor her next tour.
Terms are unclear but Pepsi said it is their biggest entertainment deal to date.
Michael Jackson earned a reported $5m (£3.4m) for his Pepsi collaboration in 1984.
Speaking at Pepsi headquarters in Purchase, New York, Spears called previous Pepsi endorsers like Jackson, soul singer Aretha Franklin, country star Faith Hill and Ray Charles "all of my heroes".
"It's such an honour," she said. "I'm a big fan of Pepsi products and Pepsi commercials.
"My life and my career have been blessed. The chance to follow some of my heroes - some incredible performers - and create something new with the innovative people at Pepsi is very exciting for me."
Dawn Hudson, Pepsi's senior vice president of strategy and marketing, said: "Britney is on the cutting edge of contemporary, popular entertainment.
"She's youthful, inventive, optimistic and fun-loving - the ultimate fit with brand Pepsi."
Other sponsorship deals
Spears' deal is likely to be more in line with current star sponsorships such as golfer Tiger Woods, who will reportedly earn $100m (£68.75m) over five years in a contract with Nike sports clothing.
Wimbledon winner Venus Williams has also just signed a contract reportedly worth $40m (£27.5m) with Reebok.
Other Pepsi promoters include British pop stars Robbie Williams, The Spice Girls and Boyzone.
Spears, who is nominated for Grammy Awards in Best Pop Vocal Album and Best Female Pop Vocal Performance categories later this month, already has sponsorship deals with footwear company Skechers.
The first Spears television commercial is expected to debut during the Oscar ceremony on ABC television.