The Restaurant Group - which also owns Garfunkel’s, Joe’s Kitchen and Chiquito - will fund the deal through a combination of cash, debt and a rights issue.
Wagamama is being sold by private equity firms Duke Street and Hutton Collins.
Restaurant Group chief executive Andy McCue said: “This transaction is an exciting and transformative opportunity to create a business which can pursue a truly multi-pronged growth strategy and create substantial value for our shareholders.
“Wagamama is a fantastic brand, with a market-leading pan-Asian proposition, which has consistently outperformed the casual dining market in recent years.
“Central to this success has been a cohesive culture and clear brand values which are focused on making the right choices for customers.”
The Restaurant Group will embark on a rights issue to raise £315 million and draw on a £220 million revolving credit facility to bankroll the deal.
Mr McCue has been overseeing a turnaround at the Restaurant Group, which has seen a revamp of pricing, food quality and marketing, as well as restaurant closures.
He now plans to accelerate the rollout of Wagamama’s across the UK, expand concessions and pilot pan-Asian cuisine “food-to-go” offerings.
The firm will also explore international growth opportunities for Wagamama.
Emma Woods, currently chief growth officer, will become the Wagamama CEO and chairman Allan Leighton will join the Restaurant Group board.
Mr McCue added: “The transaction not only gives us a great brand but also creates a business with a multi-pronged growth strategy which will enhance earnings with continued selective UK rollout, accelerated via conversions of some TRG sites; by further leveraging the brand in concessions both in the UK and internationally; by maximising the opportunities presented by the rapidly growing delivery sector; and by optimising the potential within international markets.”
The deal comes at an increasingly challenging time for the eating-out sector as it continues to suffer from a slowdown in consumer spending.