The revitalised brand sold 30,190 vehicles in June to finish 7,000 units ahead of Ford in second place, according to the latest figures from the Society of Motor Manufacturers and Traders (SMMT).
Vauxhall has attributed the boost in popularity to a strong line-up of cars and successful June sales across the UK.
"This is great news for us," said Duncan Aldred, Vauxhall’s Managing Director. "Product is king for UK buyers and our June sales prove that we’re ticking all the right boxes with customers when it comes to the quality, performance and value of our cars."
Vauxhall has seen sales of the Astra hatchback and the Corsa supermini boosted by the larger Zafira and all-new Meriva in June.
As recently as 2008, the company was struggling with falling sales, but models such as the new Corsa, and the forthcoming extended electric Ampera have boosted sales and secured the future of Vauxhall.
It was a good month for the industry as a whole, with new car registrations up by 10.8 per cent in June and 19.9 per cent in the first half of 2010.
It is the 12th successive monthly increase in new car registrations despite the end of the scrappage scheme. While smaller cars remained top of the best-sellers list, there was a rise in MPV and luxury saloon sectors compared to the same period in 2009.
"The new car market continued to perform above expectations in June, with fleet sector registrations up 25% compared to this time last year. The results indicate improved business confidence and a strengthening economic recovery," said Paul Everitt, SMMT chief executive.
However, Everitt warned new car registrations are expected to slump in the second half of the year and has called on the government to improve access to credit for customers to sustain recovery.