Modem will work on online campaigns for the car-maker's range of marques and will redesign its website, www.vauxhall.co.uk. The work will be integrated with Vauxhall's other marketing efforts including its TV and print campaigns.
The existing website covers both cars and commercial vehicles and promotes the entire Vauxhall range. Online facilities include dealer locators, test drive requests, and hints and tips for drivers.
The win, which is understood to involve a five-year relationship, strengthens the agency's grip on the General Motors account across Europe, where it also works on Opel and Chevrolet.
Chris Evans, the relationship marketing manager for General Motors in the UK, said: "We have a broad range of customers and prospects. Our website should provide for the requirements of each of our audiences. Our existing site is functionally very rich - we are looking to develop this with greater creativity, emotional engagement and features and services that are designed to help the passing trade explore our cars."