Neither Vauxhall nor Lowe were available for comment as Campaign went to press, but industry sources say the agency has beaten Delaney Lund Knox Warren & Partners and TBWA\GGT in the race for the business.
The decision halts what had been a steady migration of Vauxhall business from Lowe to DLKW.
It also marks the first inroad made by Lowe into the Vauxhall business since last year's appointment of Matthew Bull as the chief executive.
Bull was denied a dream start to his job last September when Lowe lost out to DLKW for the £12 million relaunch of the Astra. Under Vauxhall's existing agency system, its roster agencies compete for each new model launch.
Bull admitted at the time: "We have got to learn more about Vauxhall's business and get into the client's head space."
Scheduled to be unveiled at next month's Geneva motor show, the £12,000, folding hard-top Tigra, which is built in France, will compete against the Peugeot 206CC, the Mazda MX5 and the new Nissan Micra.
The two-seater model, which has a Corsa-based chassis, will go on sale in the UK, one of Europe's biggest convertible car markets, in April.
Kevin Whale, the Vauxhall chairman, said: "The Tigra plays an important role in our model offensive and shows the new direction we have taken with our product portfolio, 20 per cent of which will soon consist of niche models."
The Tigra win provides a welcome boost for Lowe, which recently lost its £40 million global Braun business to BBDO and faces a review of its above-the-line worldwide HSBC assignment.