The agencies will create an experiential push as part of the NFL's drive to bolster the appeal of the sport internationally. The Wembley game, which will be contested between the Miami Dolphins and New York Giants, will be played on 28 October.
More than 500,000 fans registered for tickets for the game within 72 hours of the details being announced, according to the NFL.
Gareth Davies, marketing director of NFL UK, said the league plans to establish itself with a 'big-statement campaign' including bursts of high-profile activity at key London locations.
The appointment is the first new-business win for Not Actual Size, an experiential specialist set up by Dan Holliday, the founder of The Fish Can Sing.