The brief includes developing its research strategy, organising online panels and surveys and tracking studies. Locog chairman Sebastian Coe said there would be a focus on the youth market.
Nielsen's appointment follows Locog's decision to appoint McCann Erickson to its advertising account. The agency beat WPP Group, tipped by many to win the account.
Coe said: "The Nielsen Company will assist us in the decision making process by testing our ideas in the marketplace.
"One of our challenges and opportunities is connecting with young people. Nielsen will help us do this."