The agency is in final discussions with Hertz following a pitch against an undisclosed number of agencies.
The main account is held by Rainey Kelly Campbell Roalfe/Y&R, which did not pitch. Hertz said it would remain as its incumbent.
RKCR/Y&R won the business in January this year and was briefed to develop a pan-European strategic campaign to bolster Hertz's brand value in a market that currently has little consumer appeal.
Since its appointment, the agency has been working on strategic planning for the brand but has not produced any work for the account in the past six months.
DDB will work on a project basis on a through-the-line campaign designed to promote its customer loyalty programme. It will focus on CRM and will include in-store, e-mail and above-the-line communications.
According to Nielsen Media Research figures, Hertz's spend in the UK last year was £1 million.
DDB declined to comment on the story.