The actress, who recently welcomed her first child with husband Max Handleman via a surrogate, was reported to have signed up to the adaptation earlier in the month and took to Twitter to confirm the news today.
Setting a teaser for her followers, Banks tweeted: "Guess who said this, 'I'm smiling at you even though you're aggravating me.'"
She later revealed: "Yes! And I can now confirm I'm EFFIE TRINKET in @TheHungerGames. So excited! RT @ohpoorsam Effie Trinket! (sic)"
The film is based on the Suzanne Collins novel of the same name and is scheduled for a March 2012 release.
In the Collins books, Effie Trinket works as a District 12 escort for lead character Katniss Everdeen and is famous for sporting brightly-coloured wigs.
Other names confirmed for the movie include Jennifer Lawrence and Josh Hutcherson.