The deal involves Emap becoming Disney's sole radio partner for the promotion of the animated film.
Emap radio logos will also feature on Disney's advertising campaigns.
The advertising activity will run across Emap's full portfolio of radio stations. Brands including Kiss, Magic, Big City network and The Hits will run advertising for Finding Nemo.
Disney will also use Emap's national digital radio package, One Nation.
An on-air promotion will offer listeners the chance to win a holiday to Australia's Great Barrier Reef as well as tickets to the film and its premiere.
Activity kicks off this week, ahead of the film's release on 10 October.
The completion of the deal with Buena Vista, which is distributing the Disney film, follows a recent cross-media agreement between Emap and United International Pictures. UIP paid £250,000 to promote American Pie: The Wedding across Emap properties including FHM and Kerrang!
Lee Jury, the senior marketing manager at Buena Vista International UK, said: "Finding Nemo will be one of the biggest movies of the year in the UK, and to achieve this we must ensure that the film is communicated to a very broad demographic.
"Working across Emap's portfolio of stations enables us to reach not only the family market for this film but the important regular cinema-going 15- to 34-year-old audience."