The £213 million deal values Brewdog at £1 billion 10 years after it was founded by James Watt and Martin Dickie.
Brewdog said £100 million from the sale would go into business expansion with the remainder going to existing shareholders.
In a statement on its website, Brewdog described the partnership with TSG as “a launch pad for us to turbocharge our mission to make the world as passionate about craft beer as we are”.
The statement, attributed to “James and the Brewdog team” sought to head off criticism that its founders were selling out on their ethos of offering an antidote to corporate big business and traditional marketing.
“This couldn’t be further than the truth,” the statement said. “We have taken on a minority investment partner, just like we did with the [alcohol industry merchant bank] Griffin Group in 2009.
"Martin and myself still control the company and remain the largest shareholders. Other great craft brewers like Stone Brewing and Dogfish Head also recently took on minority investment deals, which are very similar to the deal we have just concluded.
“TSG [is] also completely aligned with our stance on independence, and this remains entrenched into our articles of association. This deal gives us the firepower to compete globally with the mega-beer corporations and their faux craft beers, while remaining fiercely independent.”