BRG, which operates Slim Chickens, Giraffe and Ed’s Easy Diner, says the deal will save more than 600 jobs.
However, given that GBK employed nearly 1,300 staff across its estate prior to the pandemic, it is estimated that roughly the same amount will face redundancy.
"We welcome the GBK team to BRG," says Satnam Leihal, managing director of BRG.
"This latest acquisition is in line with our strategy to grow our restaurant group with quality brands.
"Whilst it is an extremely challenging time for the sector, we believe quality hospitality businesses will recover in the long term as people return to eating out.”
It was reported last month that GBK's now-former owner, the South Africa-based Famous Brands, had kicked off a process to sell the chain, having withdrawn its funding for the business in April.
Owned by Ranjit Singh Boparan, Boparan has a history of snapping up troubled restaurant business.
In May the group acquired ailing restaurant chain Carluccio's in a deal worth just £3.4m.
Its purchase of GBK gives BRG a 99-strong portfolio of restaurants nationwide, with 32 franchised globally - BRG will continue GBK’s franchise partnership in the UAE as part of the deal.
Gourmet Burger Kitchen was founded in Battersea, London in 2001 by three New Zealanders with the backing of chef Peter Gordon.
It was bought by investment firm Yellowwoods Group in 2010, leading to rapid growth of the chain; and was then subsequently acquired by Famous Brands in 2016, which led to a further period of expansion focused on regional locations outside of the chain's London heartland.
The chain eventually underwent a financial restructuring in 2018 in the form of a Company Voluntary Arrangement (CVA) , which resulted in the closure of dozens of restaurants.