A spokesman for the agency said the deal was "long-term over a number of years".
Weber Shandwick is charged with driving the social strategy, developing social-first campaigns, content creation and handling the day-to-day community management.
Chris Hawken, brand marketing director at Vauxhall, said: "We feel social media has a fundamental role to play in building our brands and driving business value. We wanted to work with an agency that really understood how to engage our key audiences – we found that in Weber Shandwick."
Adam Clyne, head of digital at Weber Shandwick, said: "Vauxhall is a brand that really understands the major opportunity that social presents from a commercial perspective. We are looking forward to partnering with it to develop campaigns with big ideas at the heart that have a real impact on business results."
The Vauxhall account will be led strategically by EMEA head of social Danny Whatmough and creatively by the agency’s recently appointed executive creative director for EMEA, James Nester.