The move comes as she prepares to compete in the Powerade Great CityGames in Manchester this weekend.
Ennis recently won gold at the IAAF World Championships and IAAF Indoor World Championships.
The deal, which runs until the end of 2012, will see Jessica work closely with Powerade and their experts in hydration and nutrition to help her perform to her maximum both in training and competition.
She says: “I’m really excited to be a part of the Powerade team. It’s great to hear some of the ideas and the direction they are taking Powerade and I can’t wait to see and taste what the future brings.”
Ennis will act as an ambassador for Powerade and will be making appearances for the Isotonic Sports Drink to help promote the benefits of hydration, as well as appearing in above-the-line marketing activity and brand endorsements.