DDB triumphed against Fallon Minneapolis and Crispin Porter & Bogusky to pick up the £15 million satellite navigation account earlier this week.
TBWA\London was also initially involved in the review, but pulled out before the pitch stage owing to conflict with Garmin's rival Tom Tom.
The TBWA network holds the Tom Tom account in continental Europe.
Garmin, which has not previously had a major advertising presence, is looking to create its first branding campaign to take it head to head with Tom Tom.
Garmin designs, manufactures and markets navigation and communications equipment for the aviation and consumer markets worldwide. The company has a 50 per cent share of the personal navigation systems market in the US.
Tom Tom is currently running a TV ad campaign in the UK. The ad features a family using the Tom Tom GPS map system in their car.
Garmin and DDB both declined to comment as Campaign went to press.